Common emotional and behavioral disorders in preschool children

Common emotional and behavioral disorders inpreschool children: presentation, nosology, and

epidemiology

Helen Link Egger and Adrian AngoldCenter for Developmental Epidemiology, Department of Psychiatry and Behavioral Sciences at Duke University

Medical Center, USA

We review recent research on the presentation, nosology and epidemiology of behavioral and emotionalpsychiatric disorders in preschool children (children ages 2 through 5 years old), focusing on the fivemost common groups of childhood psychiatric disorders: attention deficit hyperactivity disorders, op-positional defiant and conduct disorders, anxiety disorders, and depressive disorders. We review thevarious approaches to classifying behavioral and emotional dysregulation in preschoolers and deter-mining the boundaries between normative variation and clinically significant presentations. Whilehighlighting the limitations of the current DSM-IV diagnostic criteria for identifying preschool psycho-pathology and reviewing alternative diagnostic approaches, we also present evidence supporting thereliability and validity of developmentally appropriate criteria for diagnosing psychiatric disorders inchildren as young as two years old. Despite the relative lack of research on preschool psychopathologycompared with studies of the epidemiology of psychiatric disorders in older children, the currentevidence now shows quite convincingly that the rates of the common child psychiatric disorders and thepatterns of comorbidity among them in preschoolers are similar to those seen in later childhood. Wereview the implications of these conclusions for research on the etiology, nosology, and development ofearly onset of psychiatric disorders, and for targeted treatment, early intervention and prevention withyoung children. Keywords: Diagnosis, comorbidity, preschoolers, nosology, epidemiology, preval-ence. Abbreviations: ADHD: attention-deficit hyperactivity disorder; ODD: oppositional defiant dis-order; CD: conduct disorder; SAD: separation anxiety disorder; GAD: generalized anxiety disorder;PTSD: post-traumatic stress disorder; PAPA: Preschool Age Psychiatric Assessment; PTRTS: PAPATest–Retest Study (PTRTS).

In the USA the number of preschool-age childrenreceiving psychopharmacological treatment in-creased 3-fold from 1990 to 1995 (Zito, 2002; Zitoet al., 2000) and is still growing (Barbaresi, 2003;Blackman, 1999; DeBar, Lynch, Powell, & Gale,2003; Greenhill, 1998; Greenhill et al., 2003; Minde,1998; Patel, Crismon, Hoagwood, & Johnsrud, 2005;Rappley et al., 2002; Stubbe & Martin, 2000;Waters, 1990; Zito et al., 2000). These data areconcerning because our understanding of thenosology of preschool mental health disorders is stillin its infancy (Angold & Egger, 2004). While thepediatricians and psychiatrists prescribing psycho-tropic medications for preschoolers are explicitly, orimplicitly, applying some set of diagnostic criteria tothese children, there is currently no consensusabout the best criteria for defining most psychiatricdisorders in very young children (Pine et al., 2002).How are these young children being diagnosed?What criteria are being applied? Are the criteriadevelopmentally sensitive? Do they account for age-appropriate variation during this period of rapidcognitive, social, emotional and behavioral develop-ment? How do we distinguish between normativeindividual differences, temperamental variation, andclinically significant behaviors and emotions?

Answers to these questions have enormous impli-cations for early intervention/prevention efforts, aswell as for our understanding of the early emergenceof psychopathology.

With the exception of autism (Volkmar, Lord, &Bailey, 2004) and, perhaps, ADHD (for a review seeEgger, Kondo, & Angold, in press b), our under-standing of the nosology of preschool psychiatricdisorders, as well as the epidemiology of their pre-valence and course, is still far behind our under-standing of psychiatric disorders in older children(Angold & Egger, 2004). It is only very recently that afew programs of research on psychiatric disorders inpreschoolers have begun to apply standardizedmeasurement strategies (Carter, Briggs-Gowan, &Davis, 2004) familiar from the study of psycho-pathology in older children, such as reliable struc-tured diagnostic interviews (Egger & Angold, 2004),to do the type of psychiatric epidemiology and clin-ical research with preschoolers that has been donewith older children and adults.

Studies in adults using retrospective reports ofonset dates have repeatedly shown that a sub-stantial proportion of psychiatric disorders start inchildhood or adolescence (Kessler et al., 2005a; Kim-Cohen et al., 2003). Thomas Insel, current Director

Journal of Child Psychology and Psychiatry 47:3/4 (2006), pp 313–337 doi:10.1111/j.1469-7610.2006.01618.x

� 2006 The AuthorsJournal compilation � 2006 Association for Child and Adolescent Mental Health.Published by Blackwell Publishing, 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA

of NIMH, recently concluded that psychiatric symp-toms and disorders ‘begin early in life, are chronic,and protracted’ (Insel & Fenton, 2005, p. 590). Inthis paper, we will review various approaches to thecharacterization of preschool psychopathology, aswell as recent data on the most common psychiatricdisorders in preschool children. Although our un-derstanding of preschool psychopathology lags farbehind our understanding of psychopathology inschool-age children and adolescents, these datasuggest that to truly understand the ‘early onset’ ofpsychiatric disorders, we can start no later than thepreschool period.

Methods

We review the literature on preschool psycho-pathology published concerning five diagnostic areas:attention-deficit hyperactivity disorder (ADHD), op-positional defiant disorder (ODD), conduct disorder(CD), depressive disorders (major depression, dys-thymia, depression NOS/minor depression), andanxiety disorders (separation anxiety disorder (SAD),generalized anxiety disorder (GAD), social phobia,specific phobia, post-traumatic stress disorder(PTSD)). This review will not consider autism orpervasive developmental disorders, because anexcellent review was published in the 2004 JCPP

Annual Review issue (Volkmar et al., 2004).While we touch upon issues of measurement and

assessment, we also refer readers to Carter andcolleagues’ 2004 review of assessment measures foryoung children (Carter et al., 2004) and a recentbook on the mental health assessment of infants andtoddlers (DelCarmen-Wiggins & Carter, 2004), forin-depth reviews of methods and measures forassessing preschool psychopathology, as well asdiscussions of unresolved issues including methodsfor combining information from multiple informants,methods for making diagnoses in young children,methods for assessing young children’s internaldistress, and approaches to the assessment ofimpairment.

Should preschoolers be diagnosed withpsychiatric disorders?

Many researchers and clinicians wonder whether itis possible, or even desirable, to classify psychiatricdisorders in preschool children (for a review of theseconcerns see Angold & Egger, 2004; Carter et al.,2004; Emde, Bingham, & Harmon, 1993). Objec-tions to the classification of psychiatric disorders inpreschoolers arise from several concerns: (1) that thepreschool period involves such rapid physical (in-cluding neural), behavioral, emotional, and cognitivedevelopment that it is not possible to identify validsymptoms or clusters of symptoms that can be re-liably measured, (2) that individual differences in

normal development will be inappropriately identi-fied as psychiatric symptoms or disorders, (3) thatthe dominant psychiatric taxonomy, the DSM/ICDapproach, does not account for developmental var-iation, (4) that young children will be inappropriately‘labeled’ with ‘diseases’ that will adversely shape thechild’s perception of him/herself and parents’ orother caregivers’ perceptions of the child, and (5) thatproblematic behavior in very young children is notlocated ‘in the child’ but rather in the relationshipsbetween parents and children and the wider envir-onment.

Similar concerns were raised 30 years ago whenresearchers began to define the nosology of psychi-atric disorders in older children. In particular, theargument was made that depression diagnosedusing adult criteria did not occur in school-agechildren and adolescents (Rie, 1966; Sandler & Joffe,1965; Toolan, 1962). However, the operationaliza-tion of criteria for specific psychiatric disorders andsub-types of disorders and the development of reli-able measures of these criteria proved to be thecritical first steps in demonstrating the validity ofchildhood psychiatric disorders (or symptom clus-ters), including depression. That work has now al-lowed the field to move on to considering thephysiologic, neural, genetic, and environmentalcorrelates of these disorders, and their responses totreatment. For instance, the DSM criteria fordepression were found to identify a valid childhoodpsychiatric disorder which could be reliably meas-ured using structured psychiatric interviews, wasnot that uncommon, and was responsive to bothmedication and cognitive-behavioral treatment.

The significant advances in our understanding ofthe nosology, epidemiology, and neuropsychologicaland genetics correlates of autism spectrum disordersin young children have resulted from a similar sys-tematic program of research (Fombonne, 2003;Rutter, 2000; Volkmar et al., 2004). Overall, theDSM-IV diagnostic criteria have worked quite well asa means of advancing our understanding of thepresentation and course of autism spectrum dis-orders, despite their lack of developmentally specificcriteria. The dual approach of testing the applic-ability of current diagnostic criteria for identifyingautism spectrum disorders in young children, whileexploring the validity and clinical utility of develop-mentally specific criteria and/or diagnostic algo-rithms for use with young children, provides anexemplary roadmap for examining the validity ofspecific behavioral and emotional disorders inpreschoolers.

Multiple classification systems

There are different approaches and taxonomies foridentifying young childrenwith ‘at-risk,’ ‘problematic’or ‘clinically significant’ emotions and behavior.

314 Helen Link Egger and Adrian Angold

� 2006 The AuthorsJournal compilation � 2006 Association for Child and Adolescent Mental Health.

Historically, young children’s affective andbehavioraldysregulation has been approached dimensionally,with cutpoints set to characterize subsets of childrenat the extreme of the distribution of (1) normative be-haviors and emotions and/or (2) temperament traits.In these models, extremes of problems or tempera-ment traits have typically been regarded as precur-sors of, or risk factors for, later psychopathology,rather thanasmanifestations of psychiatric disorderssimilar to those identified at later stages of life. Dia-gnostic classifications of preschool psychopathology,categorical approaches,haveeitherused (1) theDSM/ICD nosology, either unmodified or modified to bedevelopmentally appropriate for young children (e.g.,the Research Diagnostic Criteria-Preschool Age (TaskForce on Research Diagnostic Criteria: Infancy andPreschool, 2003)), or (2) theDiagnostic Classification:0–3 (DC:0–3), an alternative system for classifyingmental healthdisorders in infant and toddlers (Zero toThree, 1994, 2005). These categorical approachesseek to identify clinically significant syndromes,characterized by severity, pervasiveness, persistence,and impairment, that are, themselves, early-onset‘disorders,’ rather than simply risk factors for laterdisorders. None of these approaches to preschooldysfunction has established its superiority overthe others. Each provides a particular windowinto understanding the phenomena of problematicbehavioral and emotional dysregulation in pre-schoolers.

Dimensional approaches

Checklist measures and ‘clinically significant’ cut-points on symptom scales. A number of studies,from the 1940s on, demonstrated that individualsymptoms including aggression, oppositionality,hyperactivity, fears, and social anxiety were commonin young children (Cummings, 1944; Earls, 1980;Griffiths, 1952; Loeber & Stouthamer-Loeber, 1997;MacFarlane, Allen, & Honzik, 1954; Marks, 1987;Richman et al., 1974; Tremblay, 2004). An import-ant contribution of these studies was the descriptionof the distribution of normative and problematicbehavior in non-clinical samples of children and thevariation in their presentations from toddlerhood tokindergarten entry. The careful description of be-haviors and their frequencies and other qualities ateach age in non-clinical populations is a necessaryfirst step. This descriptive work makes it possible todesignate empirically-determined cutpoints andidentify non-normative clusters of symptoms.

More recently, studies of preschoolers have usedchecklist measures to define specific types of dis-ordered groups of young children. These measuresinclude ‘empirically-derived’ checklists such as theChild Behavior Checklist (CBCL) 1½ –5 (Achenbach& Rescorla, 2000), DSM-referenced rating scalessuch as the Early Childhood Inventory-4 (ECI) (Ga-dow & Sprafkin, 1997, 2000; Gadow, Sprafkin, &

Nolan, 2001; Sprafkin & Gadow, 1996), or checklistmeasures of specific symptom clusters such as theADHD Rating Scale (DuPaul, Power, Anastopoulos,& Reid, 1998; Gimpel & Kuhn, 2000) or thePreschool Anxiety Scale (PAS) (Spence, Rapee,McDonald, & Ingram, 2001). Although checklistmeasures like these do not include enough symptomspecificity (e.g., frequency, duration, onset) to enableresearchers or clinicians to make the sorts of psy-chiatric diagnoses that we are familiar with at everyother stage of life, they have been informative in anumber of ways: (1) They show that relatively stablepsychopathological characteristics can be reliablyidentified in preschoolers (consider, for instance, theencouraging psychometric properties of the CBCL1½–5 (Achenbach & Rescorla, 2000) and the EarlyChildhood Inventory (ECI) (Gadow & Sprafkin,1997)). (2) They have estimated the overall pre-valence of ‘problematic’ preschool behavior atsomewhere between 7% and 25% (Earls, 1980; Earlset al., 1982; Earls & Richman, 1980a; Earls &Richman, 1980b; Jenkins, Bax, & Hart, 1980; Koot& Verhulst, 1991; Richman, 1977; Richman, Ste-venson, & Graham, 1982; Richman et al., 1974;Stevenson, Richman, & Graham, 1985; Thomas,Byrne, Offord, & Boyle, 1991), rates quite similar tothose reported in early questionnaire studies ofsymptoms in older children (for a review see Achen-bach & Edelbrock, 1978). (3) They have consistentlyidentified distinct emotional (internalizing) and be-havioral (externalizing) syndromes (Achenbach,Edelbrock, & Howell, 1987; Achenbach & Rescorla,2000; Behar & Stringfield, 1974; Crowther, Bond,& Rolf, 1981; Koot, van den Oord, Verhulst, &Boomsma, 1997; Koot & Verhulst, 1991; McGuire &Richman, 1986; Richman et al., 1982; van den Oord,Koot, Boomsma, Verhulst, & Orlebeke, 1995). (4)They have provided strong evidence of continuitybetween preschool behavioral and emotional prob-lems and psychopathology in later childhood(Campbell & Ewing, 1990; Campbell, Ewing, Breaux,& Szumowski, 1986; Earls, 1980; Fischer, Rolf,Hasazi, & Cummings, 1984; Keenan, Shaw, Delli-quadri, Giovannelli, & Walsh, 1998; McGee, Part-ridge, Williams, & Silva, 1991; Mesman & Koot,2000; Mesman & Koot, 2001; Richman et al., 1982;Shaw, Owens, Giovannelli, & Winslow, 2001), andeven adulthood (Caspi, Moffitt, Newman, & Silva,1996; Stevenson & Goodman, 2001). (5) They haveidentified clusters of symptoms that map onto thebroad and specific DSM diagnostic categories (e.g.,CBCL 1½–5 DSM-oriented scales (Achenbach &Rescorla, 2000) and ECI DSM-referenced syndromes(Gadow & Sprafkin, 1997, 2000; Gadow et al., 2001;Sprafkin & Gadow, 1996)). (6) They have been thebasis for demonstrations of the heritability of certainpreschool behaviors and emotions (van den Oordet al., 1995; van den Oord, Verhulst, & Boomsma,1996), including differentiated clusters of anxietysymptoms (Eley et al., 2003).

Preschool psychopathology 315


Preschool temperaments as risk factors for psychi-atric disorders later in childhood and adult-hood. For 40 years temperament research hasgenerated findings of great relevance to preschoolpsychopathology. The concept originated in the fieldof infancy research (Rutter, Birch, Thomas, & Chess,1964; Thomas & Chess, 1977), but has now ex-tended its reach into adulthood to cover formula-tions of a putative small number of dimensions withwide-ranging impacts on emotions, behavior, andpsychopathology (e.g., Battaglia, Przybeck, Bellodi,& Cloninger, 1996; Ono et al., 2002; Wills, Windle, &Cleary, 1998). Although various conceptualizationsof temperament have been proposed, each systemshares common elements: Temperament character-istics are individual differences in reactivity andregulation that are constitutional (i.e., inherited,biological, physiological), present early in life, andrelatively stable, although influenced by maturationand experience (Buss & Plomin, 1975; Goldsmithet al., 1987; Rothbart & Bates, 1998; Thomas &Chess, 1977). Broad temperament dimensions,particularly negative affectivity (which resemblesadult neuroticism), and extreme temperament types,particularly behavioral inhibition and behavioraldisinhibition, have been identified as risk factors forthe development of psychiatric disorders later inchildhood and adulthood, and have been shown tobe concurrently associated with problematic beha-viors in preschoolers.

Like the broad internalizing scale of the CBCL,negative affectivity is a global measure of a range ofnegative emotions including sadness, fear, anger,frustration, poor adaptability, and high emotionalintensity (Buss & Plomin, 1984; Rothbart, Ahadi,Hersey, & Fisher, 2001; Rowe & Plomin, 1977;Thomas & Chess, 1977). Preschool negative affec-tivity has been found to predict later childhood ex-ternalizing and internalizing symptoms (Bates &Bayles, 1988; Caspi et al., 1995; Caspi & Silva,1995; Earls, 1982b; Earls & Jung, 1987; Gjone &Stevenson, 1997; Goldberg, Corter, Lojkasek, &Minde, 1990; Goldsmith & Lemery, 2000; Goodyer,Ashby, Altham, Vize, & Cooper, 1993; Rende, 1993;Sanson, Oberklaid, Pedlow, & Prior, 1991; Schmitzet al., 1999; Shaw, Keenan, Vondra, Delliquadri, &Giovannelli, 1997), as well as antisocial behavior inadulthood (Henry, Caspi, Moffitt, & Silva, 1996;Moffitt, Caspi, Dickson, Silva, & Stanton, 1996). Afew studies of preschoolers have linked negativeaffectivity to concurrent measures of overall problembehaviors (Earls, 1982b; Earls & Jung, 1987),internalizing and externalizing syndromes (Guerin,Gottfried, & Thomas, 1997; Lee & Bates, 1985;Maziade, Cote, Bernier, Boutin, & Thivierge, 1989;Maziade, Cote, Thivierge, Boutin, & Bernier, 1989;Shaw, Owens, Vondra, Keenan, & Winslow, 1996),and symptoms of anxiety and depression (Keenanet al., 1998; Kingston & Prior, 1995; Shaw et al.,1997; Wolfson, Fields, & Rose, 1987).

Patterns of temperament traits in preschoolershave also been linked to increased risk for laterpsychiatric disorders. The two extreme temperamenttypes of behavioral inhibition (BI) and behavioraldisinhibition/exuberance (BD) have been well char-acterized in infants and young children (for a reviewsee Hirshfeld-Becker et al., 2003). Distinct patternsof biological arousal and reactivity underscore thedifferences in emotion regulation underlying thesetwo patterns of temperamental emotionality (Derry-berry & Rothbart, 1997; Fox, Henderson, Rubin,Calkins, & Schmidt, 2001; Fox, Schmidt, Calkins,Rubin, & Coplan, 1996; Gray, 1982). BI, identified inabout 15% of preschoolers (and young rhesus mon-keys), is associated with shyness, fear, withdrawal innovel situations, and anxious/fearful distress. BI isheritable, associated with parental anxiety dis-orders, has physiological accompaniments(sympathetic, cardiovascular, and cortisol hyper-reactivity), and is a risk factor for anxiety disordersand depression later in childhood and adulthood(Adamec & Stark-Adamec, 1989; Biederman et al.,1993; Biederman, Rosenbaum, Chaloff, & Kagan,1995; Caspi et al., 1996; DiLalla & Falligant, 1995;DiLalla, Kagan, & Reznick, 1994; Fisher, Kagan, &Reznick, 1994; Hirshfeld, Biederman, Brody, Fara-one, & Rosenbaum, 1997; Hirshfeld et al., 1992;Hirshfeld-Becker et al., 2003; Nachimias, Gunnar,Mangelsdorf, Parritz, & Buss, 1996; Suomi, 1999).BI’s inverse, BD, is characterized by high approach,high novelty seeking, low harm avoidance, andirritable distress. BD is a putative risk factor forADHD, disruptive behavioral disorders (DBDs),comorbid DBDs and mood disorders, and aggressivebehaviors (Caspi et al., 1995, 1996; Caspi &Silva, 1995; Hirshfeld-Becker et al., 2002; Raine,Reynolds, Venables, Mednick, & Farrington, 1998;Rubin, Burgess, Dwyer, & Hastings, 2003; Tremblay,Pihl, Vitaro, & Dobkin, 1994).

Although temperamental characteristics havebeen conceptualized as risk factors for a variety ofpsychiatric disorders across the lifespan, it is alsopossible that early-measured temperamental char-acteristics could represent the early presence of thedisorders themselves. The lack of conceptual clarityabout the distinction between temperament andpsychopathology is reflected in the number of over-lapping items in temperament and psychopathologymeasures. Such overlap presents a serious methodo-logical and conceptual problem for understandingthe relationship between temperament and early-onset psychopathology (Frick, 2004). For example,24 items of the 94-item Child Behavior Ques-tionnaire (CBQ) (Rothbart et al., 2001), a commonlyused early childhood temperament scale, are iden-tical to or direct opposites of items on the CBCL. AsLahey has pointed out, naming certain behaviors‘temperament traits’ and other behaviors (or even thesame behaviors) ‘psychiatric symptoms’ is not an actinherently reflective of nature, but rather reflects



distinctions stemming from particular theoreticalperspectives (Lahey, 2004). Both perspectives reflectthe fact that there is a continuum between develop-mentally normative behaviors and emotions, indi-vidual (temperamental) variations and clinicallysignificant symptoms, with gradations based onpatterns of distribution, intensity, frequency, dur-ation, persistence, and impairment.

At this point, it seems plausible that some ‘ex-tremes of temperament’ could qualify as psychiatricdisorders (e.g., some behaviorally inhibited pre-schoolers may meet criteria for DSM-defined socialphobia), but extremity on a temperament dimensionis neither a necessary nor a sufficient condition forthe identification of a psychiatric disorder. Psychi-atric disorders include many symptoms that are notincluded in any temperament assessment, particu-larly at the severe end of the spectrum, and so, froma measurement perspective, the temperamentalapproach does not cover many clinically significantphenomena. Hence, temperament constructs do notprovide a conceptual framework for the full range ofpsychopathology and clinical need. To our know-ledge, no preschool study has yet assessed tem-perament characteristics and the full range ofpsychiatric symptoms, disorders, and impairmentsconcurrently, and accounted for measurement over-laps between the two approaches. But that is what isneeded if we are to compare classifications in termsof psychiatric disorders (based either on clinicallysignificant cutpoints on symptom scales or diag-nostic classifications) with classifications based ontemperament traits and types.

Diagnostic approaches

As we noted above, there has been persistent con-cern that diagnosis of psychiatric disorders inpreschoolers is ‘inappropriate’ because it ‘over-pathologizes’ and ‘medicalizes’ normal variation,individual differences, transient perturbations, andrelationship disturbances (Burke, 2003; McClellan &Speltz, 2003). Clearly, as we have already shown,there is a real and substantial challenge in distin-guishing between developmentally normal behaviorsor affect states, temperamental variation and clini-cally significant problems in very young children,although we would argue that this difficulty is notunique to this age period. On the other hand, clearlydefined, clinically valid disorders that can be reliablyassessed are essential for clinical practice. There hasbeen a longstanding debate in the child psychiatricliterature whether psychopathology in children is‘dimensional’ with clinically significant problemsrepresenting the extreme end of a continuum or‘categorical’ with individuals either meeting criteria(‘cases’) or not meeting criteria for a specific disorder(‘non-cases’) (Achenbach, 1991; Arend, Lavigne,Rosenbaum, Binns, & Christoffel, 1996; Pickles &Angold, 2003; Sonuga-Barke, 1998). However,

clinical evaluation and intervention requires that theclinician decide whether to treat or not to treat achild. Whether ‘caseness’ is defined using a cutpointon a dimensional measure or application of dia-gnostic criteria, a categorical decision must be made.From the medical point of view, this decision is calledmaking a diagnosis. Echoing Pickles and Angoldfrom their paper on this topic, the central question isnot whether symptomatology in preschoolers is bestconceptualized as scalar or categorical, but rather‘under what circumstances’ (Pickles & Angold, 2003,p. 529) it is useful to measure and define clinicallysignificant behaviors and affects from dimensionaland categorical points of view.

The DSM-IV-TR (American Psychiatric Associ-ation, 2000) and ICD-10 (World Health Organization,1992) are the dominant psychiatric classificationsystems used around the world. Because of thesimilarity between the DSM and ICD systems, as wellas the lack of studies of ICD criteria in preschoolers,this review will focus on the DSM-IV-TR criteria. TheDSM-IV-TR (as well as the preceding DSM versions)was developed with essentially no attention to theemotional and behavioral problems of preschoolers.A few DSM disorders include criteria specific tochildren (e.g., irritability can be the primary moodstate for the diagnosis of childhood depressive dis-orders). A few DSM disorders require that the dis-order have its onset during early childhood (e.g., theonset of some impairing ADHD symptoms must bebefore the age of 7). The DSM does include a separatesection entitled ‘Disorders Usually First Diagnosedin Infancy, Childhood, or Adolescence.’ Nonetheless,none of these childhood designations are specific tovery young children (except young children’s exclu-sion from a diagnosis of enuresis until age 5 orencopresis until age 4).

Recently, infant and preschool mental healthresearchers, sponsored by the American Academy ofChild and Adolescent Psychiatry, proposed modifi-cations of DSM diagnostic criteria for use with pre-school children. These modifications were publishedin2003as theResearchDiagnosticCriteria-PreschoolAge (RDC-PA) (Task Force on Research DiagnosticCriteria: Infancy and Preschool, 2003). RDC-PAis available at http://www.infantinstitute.org. Thepurpose of the RDC-PAwas to define clearly specified,developmentally appropriate criteria for preschoolpsychopathology soas to facilitate further researchonthe diagnostic validity of psychiatric disorders inpreschoolers, just as the research diagnostic criteriapublished in 1978 (Spitzer, Endicott, &Robins, 1978)led to the operationalized diagnostic criteria in theDSM-III and research on the reliability and validity ofthe psychiatric nosology for adults and then childrenand adolescents.

The Diagnostic Classification: 0–3 takes a differentapproach from the RDC-PA, with a primary goal ofclassifying disorders in infants and toddlers that arenot covered in the DSM system (Emde, 2003).



Despite its title, the DC: 0–3 has commonly beenused with children from birth through age five. TheDC: 0–3 includes alternative versions of DSM-IVdiagnoses (e.g., for anxiety and depressive dis-orders), new diagnostic categories (e.g., regulatorydisorders and parent–child relationship disorders),and a revised multi-axial system that places rela-tionship disorders on Axis II and the child’s ‘func-tional emotional developmental level’ on Axis V (Zeroto Three, 1994). A lack of operationalized criteria, aswell as a lack of boundaries between many of thedisorders (e.g., regulatory disorders and many of theother disorders), has limited research on DC: 0–3disorders, although a start has been made (e.g.,Boris, Zeanah, Larrieu, Scheeringa, & Heller, 1998;Cordeiro, Caldeira da Silva, & Goldschmidt, 2003;Guedeney et al., 2003; Keren, Feldman, & Tyano,2003; Reams, 1999; Scheeringa, Zeanah, Drell, &Larrieu, 1995; Stafford, Zeanah, & Sheeringa, 2003;Thomas & Clark, 1998) Despite this lack of adequatevalidation, DC: 0–3 is widely used in service settings,reflecting the clinical need for a developmentallyappropriate approach to classifying clinically signi-ficant behaviors in young children. A revised versionof DC: 0–3 (DC: 0–3R; Zero to Three, 2005) waspublished in August 2005. Studies comparingunmodified DSM criteria with the RDC-PA and DC:0–3R criteria are a necessary, but as yet unrealized,first step toward the development of an integrated,developmentally sensitive classification of psycho-pathology across the lifespan.

Preschool psychiatric disorders

With these issues in mind, we now turn to a review ofthe epidemiology of behavioral disorders (ADHD,ODD, and CD) and emotional disorders (anxietydisorders and depression) in preschool children. Wewill start with overall prevalence rates and thendiscuss specific diagnostic categories, concludingwith data on comorbidity. As far as possible, we willfocus on studies conducted in community samplesor primary care pediatric clinics, rather than thoserecruited from mental health clinics. Patientsattending specialty mental health clinics are knownto be a biased subset of children with more disor-ders, greater symptom severity, and greater impair-ment than children with disorders in the generalpopulation (Costello & Janiszewski, 1990; Goodmanet al., 1997). Thus, community samples are neededto address questions about nosology, comorbidity,and risk. Although representative general populationsamples are ideal (but expensive), randomly selectedgeneral pediatric primary care samples are alsoacceptable because rates of psychiatric disorder inolder children and adolescents in randomly selectedgeneral pediatric primary care samples have beenfound to be similar to general population prevalencerates (e.g., Costello et al., 1988; Horwitz, Leaf,

Leventhal, Forsyth, & Speechley, 1992). It is highlyplausible that the same will be true of preschoolpediatric primary care samples. We will review thedata from four non-specialty-clinic studies of pre-school psychiatric disorders that separately reportdata on specific psychiatric disorders in preschoolchildren (Angold, Egger, Erkanli, & Keeler, sub-mitted; Earls, 1982a; Keenan, Shaw, Walsh, Delli-quadri, & Giovannelli, 1997; Lavigne et al., 1996).We will also review relevant high-risk studies using acase-control design, which have contributed to ourunderstanding of the presentation and correlatedfeatures of specific disorders in this age group.

Community or primary care clinic studies ofpreschool psychiatric disorders

We identified four studies assessing the full range ofDSM-like psychiatric disorders in community orprimary care samples of preschool children. Earls’study was far ahead of its time, using questionnairesfollowed by clinical judgment based on the DSM-IIIcriteria to assess the rates of psychiatric disorders inall of the 3-year-old children (N ¼ 100) living onMartha’s Vineyard (Earls, 1982a). Fifteen years laterKeenan and colleagues studied another small sam-ple, this time of children living in poverty. Mothers of104 five-year-olds were administered the K-SADSand DSM-III-R diagnoses in the children were made(Keenan et al., 1997).

The first reasonably large-scale epidemiologicdiagnostic investigation of preschoolers has beenreported in a series of papers beginning in 1996 byLavigne and his colleagues (Arend et al., 1996; Dietz,Lavigne, Arend, & Rosenbaum, 1997; Lavigne et al.,1998a, 1998b, 1998c, 1994, 1999, 1998d, 1993,1996; Lavigne, Schulein, & Hahn, 1986). Using atwo-stage design, the CBCL was administered to3,860 (79% of eligible parents) parents of childrenaged 2 through 5 years visiting one of 68 Chicagoarea pediatricians. From this sample, 191 childrenwho scored at 90% or above on the CBCL and 319matched ‘low scorers’ (total N ¼ 510) were thenreassessed with the CBCL and a number of othermeasures including the Rochester Adaptive BehaviorInventory and play observation of the child. Twopsychologists independently reviewed the protocol(but did not conduct a clinical interview) and usedtheir ‘best estimate’ to make DSM-III-R diagnoses;56.3% of the families eligible for the second stageevaluation participated, resulting in an overallresponse rate of only 44.5% (Lavigne et al., 1996).

Themost recent study, the PAPA Test–Retest Study(PTRTS), was conducted by the authors of this review(for more details about the design of the study seeAngold et al., submitted; Egger et al., in press a). ThePTRTS was a screen-stratified, two-stage study withsubjects recruited from a large primary care pediatricclinic serving families from diverse ethnic and socio-economic backgrounds. Over an 18-month period,



1,073 parents of children aged 24–71 months oldattending the clinic for well-child and sick child visitscompleted the CBCL, and high scorers were over-sampled to produce a final sample of 307 childrenwhose parents were interviewed. The overall protocolcompletion rate from initial screening contact in theclinic to completion of the second PAPA interview was70%. Data is weighted back to the screening popu-lation to obtain unbiased general pediatric clinicestimates of (1) the normative range of emotional andbehavioral symptoms in children ages 2–5 years oldand (2) the diagnostic reliability and prevalence ofpsychiatric disorders in young children.

All of these studies have limitations: a high refusalrate may have affected the representativeness ofLavigne’s (1996) sample; only one study used adiagnostic measure with adequate psychometricproperties for use with preschoolers (Egger et al.,submitted-b); and two obtained data only from par-ent reports (Egger et al., submitted-b; Keenan et al.,1997).

Overall prevalence

Table 1 shows the prevalence rates of DSM disordersfrom the four available studies of preschoolers innon-psychiatric settings. These rates are approxi-mations of expected general population rates. In allbut the Lavigne study, the rates of preschool emo-tional and behavioral disorders were roughly equal.The much lower rates of anxiety disorders anddepression in the Lavigne study were coupled with amuch higher rate of ODD (16%). It is possible thatthe low response rate (45%), and the use of clinicalconsensus, rather than a structured diagnosticinterview and specified diagnostic algorithms, in theLavigne study may have resulted in a substantialbias in favor of the diagnosis of ODD, and againstemotional disorders (Lavigne et al., 1996).

Figure 1 compares the rates of overall and specificpsychiatric disorders found in the PTRTS with themedian rates in children 5–17 obtained from com-munity studies of psychopathology in childhood andadolescence from 1993 to 2005 (Costello, Egger, &Angold, 2005) and with the rates reported for adults18 or older in the National Comorbidity SurveyReplication (NCS-R) (Kessler & Wai Tat Chiu, 2005).The first thing to note is that the overall rates ofpsychiatric disorders across the four preschoolstudies (ranging from 14–26.4%; mean: 19.5%) aresimilar to the overall rate of disorders reported forolder children. Second, as has been shown repeat-edly in studies of older children and adults (Caninoet al., 2004; Kessler & Wai Tat Chiu, 2005; Shaffer,Fisher, Dulcan, & Davies, 1996), the prevalence rateof preschool disorders falls when impairment is arequired criterion. The preschool rates of ‘seriousemotional disturbance’ (SED), psychiatric disorder(s)that are associated with significant impairment (USGovernment, 1993), were again quite similar to therates in older children (12.1% and 9.1% in the PTRTSand the Lavigne study respectively, compared with amedian rate across community studies of 13.2% inolder children and adolescents (Costello et al., 2005)and 15.6% (those with severe or moderate impair-ment associated with a psychiatric disorder) inadults (Kessler & Wai Tat Chiu, 2005)).

These compared rates in Figure 1 are all cross-sectional and thus cannot be said to reflect patternsof change across the lifespan. Nonetheless, they dosuggest that while the overall rate of disorders, par-ticularly those associated with impairment, aresimilar across the lifespan, the pattern of specificdisorders varies with age. In particular, we notevariation in the prevalence of specific anxietydisorders with the expected decrease in SAD. Wealso see an increase in the rates of depression anddecrease in the rates of ODD and CD with age. The

Table 1 Prevalence of DSM disorders in preschoolers, non-specialty-referred samples

Assessment

Angold et al.(DSM-IV), N ¼ 307

Lavigne et al.(DSM-III-R), N ¼ 510

Keenan et al.(DSM-III-R), N ¼ 104

Earls(DSM-III), N ¼ 100

PAPAClinical

ConsensusUnmodifiedK-SADS

Questionnaire andclinical consensus

ADHD 3.3% 2.0% 5.7% 2%ODD 6.6% 16.8% 8.0% 4%CD 3.3% – 4.6% 0Depression 2.1% 0.3% 1.1% 0SAD 2.4% 0.3% 2.3% 5%GAD 6.5% 0.5% – –Social phobia 2.1% – 4.6% 2%Specific phobia 2.3% 0.7% 1.5% 0PTSD 0.6% 0.6% – –Selective mutism 0.6% – – –Any anxiety disorder 9.4% – – –Any emotional disorder 10.5% – 14.9% –Any behavioral disorder 9.0% – 14.9% –Any disorder 16.2% 21.4% 26.4% 14%SED 12.1%a 9.1%b – –

SED: serious emotional disorder (aDSM criteria plus impairment; bDSM criteria plus CGAS score <60).



consistent rates of ADHD in the preschool period,later childhood, and adulthood are quite striking,particularly in light of the fact that the field has onlyrecently recognized and developed tools to measureADHD in early childhood and adulthood. At thispoint in time we can only present these comparisonsas a crude cross-sectional snapshot because dataare not currently available to enable us to addresscritical questions about homotypic and heterotypiccontinuity between preschool psychiatric disordersand later childhood and adult disorders.

Impairment

In the DSM, some disorders require impairment (e.g.,ADHD, selective mutism), while many others requireeither distress or impairment (e.g., SAD, depression).Lavigne and colleagues have not directly reportedrates of impairment. In Keenan and colleagues’study, 91.3% of children with any psychiatric dis-order, 100% of those with a behavioral disorder, and84.6% of those with an emotional disorder were im-paired (based on a Global Assessment of Functioning(GAF) score of 60 or less), compared with 15.5% ofthose children without a disorder (Keenan et al.,

1997). In the PAPA, disability (impairment) frompsychiatric symptoms is assessed separately fromthe symptoms themselves, so that the relationshipbetween individual symptoms and syndromes andimpairment can be examined. In the PTRTS, all of thedisorders were significantly associated with impair-ment. Overall, 74.5% (mean impairment score of 9.6)of preschoolers with any psychiatric disorder wereimpaired compared with 9.3% of those without adisorder (mean impairment score of 0.6) (OR ¼ 21(10, 44); p < .0001) (Angold et al., submitted).

While these strong associations between symptomclusters (‘diagnoses’) and impairment provide sup-port for the validity of these diagnostic entities, boththe Keenan study and PTRTS found that preschoo-lers with sub-syndromal disorders (missing diag-nostic criteria by one or two symptoms) were alsohighly impaired, a finding that has also been repor-ted for older children (Angold, Costello, Farmer,Burns, & Erkanli, 1999b). For example, in thePTRTS, while the DSM-IV-TR six-symptom cutpointidentified a group of children who were significantlyimpaired, these children were different in degree, nottype, from children with sub-threshold ADHD. Ashas been reported in studies of older children

0% 5% 10% 15% 20% 25% 30%

PTSD

Specific phobia

Social phobia

GAD

SAD

Any Anxiety Disorder

Depression

Conduct disorder

Oppositional DefiantDisorder

ADHD

Serious EmotionalDisturbance

Any PsychiatricDisorder

Adults Children ages 5-17 Preschoolers ages 2-5

Figure 1 Prevalence of psychiatric disorders in preschoolers, children and adolescents, and adults. Data abstractedfrom: Angold, Egger, Erkanli, & Keeler, submitted; Costello, Egger, & Angold, 2005; Kessler, Chiu, Demler, & Wal-ters, 2005b.



(Angold et al., 1999b; Costello, Angold, & Keeler,1999; Pickles et al., 2001) and preschoolers (Laheyet al., 2004, 1998), there was a linear relationshipbetween the number of ADHD symptoms andimpairment. Each additional ADHD symptom dou-bled the chance that the child would also beimpaired (Egger et al., submitted-b). This relation-ship between sub-threshold ADHD and impairmentillustrates the importance of combining dimensionaland categorical approaches to identifying childrenwith clinically significant symptoms and challengesthe assumption that diagnostic status is the mostclinically useful way to identify children in need ofmental health services.

Age effects

While many DSM diagnostic criteria specify that thesymptoms must be ‘developmentally inappropriate,’no further guidance is provided about how to deter-mine the boundary between what is developmentally‘appropriate’ and ‘inappropriate.’ The conflicting re-sults about the effect of age on the prevalence ofdisorders in preschoolers in the Lavigne study andthe PTRTS provide an opportunity to examine thechallenge of identifying developmentally appropriatediagnostic criteria that account for age and develop-mental differences across the preschool period andbetween preschoolers and older children.

Age differences within the preschool period. In theLavigne study, psychiatric disorders increased inprevalence from age two to three years old and thendeclined from age four to five years old. Most of thisdifference was accounted for by an initial increase inoppositional symptoms and ODD at age 3 followed byadecline.TheprevalenceofODDwas22.5% in3-year-olds and 15% in 5-year-olds (Lavigne et al., 1996).However, the overall high rate of ODD in this sample(nearly 17% comparedwith amean of 6.2%across thethree other studies) raises the question whether theirODD diagnosis is truly indexing ‘developmentallyinappropriate’ oppositional behaviors. Because thesesymptoms were not identified using a structuredinterview (whichwecould examine tounderstandhowthe ODD symptoms were defined and assessed) and

because the diagnostic algorithms are not available,we cannot answer this question.

In thePTRTSwe foundasimilar peakof problematicbehaviors (as well as affect dysregulation) in 3-year-olds, leading us to agree with Lavigne that the ‘terribletwos’ should really be the ‘terrible threes’ (Tremblayand colleagues have found a similar peak of aggres-sion at age 3 (Tremblay, 2004)). Nonetheless, we didnot find a similar peak of disorders at age 3. Wefound no significant differences in the prevalence ofODD for toddlers (2- and 3-year-olds) compared witholder preschoolers, nor did we find a significant ageeffect when age was entered into the model as a con-tinuous variable. These data led us to use the samesymptom cutpoints and diagnostic algorithms fordiagnosing ODD across the preschool period with thePAPA. In the future, larger samples, multi-modal,multi-informantassessments, and longitudinal studydesignswill enableus to continue to examine theneedfor age (or developmental level) specific diagnosticalgorithms for ODD and other disorders.

Age differences between preschoolers and olderchildren. The DSM states that the symptoms of ODDmust occur ‘often’ or ‘more frequently than is typic-ally observed in individuals of comparable age anddevelopmental level’ (American Psychiatric Associ-ation, 2000).

Using the same approach used in the Great SmokyMountain Study of older children (Angold & Costello,1996), we operationalized ‘often’ as specified in theODD criteria as a frequency at or above the 90th per-centile for preschoolers. Table 2 illustrates that if wehad used the cutpoint that identified the 90th per-centile in the GSMS for older children, then we wouldhave vastly overdiagnosed ODD symptoms in pre-schoolers, because, as noted above, many of thesebehaviors aremore common in young children. Thesedata also show that there is great variation infrequency across the symptoms, suggesting that a

priori cutpoints incorporated into a number of symp-tom and diagnosticmeasures (e.g., coding a symptompresent if it occursmore than three times aweek)maywell be incorrect. This example illustrates theimportance of setting symptom cutpoints based onthe distribution of the behavior in the whole popula-

Table 2 Comparison of frequency cutpoints to define ODD symptoms for preschoolers

ODD symptom90th % frequencyfor older children

Prevalence forpreschoolers

using cutpointsfor older children

Empirically derived90th % frequencyfor preschoolers

Often loses temper At least 2 times/week 30.1% 2–3 times/dayOften argues with adults At least 2 times/week 7.7% 2 times/weekOften actively defies At least 2 times/week 57.1% 5 times/dayOften deliberately annoys people At least 4 times/week 11.1% 5 times/weekOften blames others > once in 3 months 26.7% Once a weekOften touchy or easily annoyed At least 2 times/week 3.4% > once in 3 monthsOften angry and resentful At least 4 times/week 20.7% Once a dayOften spiteful or vindictive > once in 3 months 10.3% >3 times in 3 months



tion, rather than asking the parent or other informantto decide if the behavior ‘often’ occurs or is abnormal.

We present this example as one approach tooperationalizing the DSM ODD criteria for youngchildren, a first step toward characterizing empiric-ally-derived constellations of abnormal disruptiveand oppositional behaviors in preschoolers.

Gender effects

Of the four preschool studies reviewed here, only theLavigne study and PTRTS examined gender differ-ences in the prevalence of overall and specific dis-orders in preschoolers. Lavigne and colleagues foundthat boys were more likely to have a psychiatricdisorder, with this difference being generated largelyby ODD. The rate of ‘pure’ ODD was twice as high forboys, while the rate of ‘comorbid ODD’ was similar inboys and girls (Lavigne et al., 1996). There were nogender differences in the rates of emotional disorders(Lavigne et al., 1996). In the PTRTS, there were nosignificant gender effects on the prevalence of any ofthe five disorders (ODD, CD, ADHD, any anxietydisorder, depression), specific anxiety disorders, or‘pure’ versus comorbid ODD. There was a trendsuggesting that boys were more than twice as likelyas girls to meet criteria for ADHD (4.7% vs. 1.8%;OR ¼ 2.7 (.9, 7.8), p ¼ .07) (Angold et al., submit-ted). A look at the ADHD sub-types revealed thatcombined type ADHD was much more common inboys than girls (2.7% vs. 0.3%; OR ¼ 9.7 (1.1, 83);p ¼ .04), while hyperactive-impulsive type wasequally common in boys and girls (2.0% vs. 1.5%;OR ¼ 1.3 (.4, 4.4); p ¼ .7) (Egger et al., submitted-b).

Specific psychiatric disorders

We now turn to a review of data on specific behavi-oral and emotional disorders diagnosed in pre-schoolers. Most of the work on specific preschoolpsychiatric disorders has been conducted with ‘high-risk’ children recruited from specialty mental healthclinics. Results from these studies will be includedin this review because of the relative paucity of dataon specific psychiatric disorders in community orprimary care samples of preschoolers.

Behavioral disorders

The vast majority of work on preschool psycho-pathology has focused on ADHD and the disruptivebehavior disorders, ODD and CD.

ADHD. ADHD appears to be the most commondiagnosis received by young children referred formental health services (Gadow et al., 2001; Keenan& Wakschlag, 2000; Wilens et al., 2002b). Forinstance, 86% of 200 preschoolers consecutively re-ferred to an academic child psychiatry clinic were

diagnosed with ADHD (Wilens et al., 2002b). TheDSM-IV-TR states that the child’s inattention and/orhyperactivity-impulsivity must be severe, frequent,persistent, and ‘inconsistent with developmentallevel’ to be considered a symptom of ADHD. Forpreschoolers, who are developing the capacity tosustain attention (Jones, Rothbart, & Posner, 2003)and inhibit behavior (Diamond & Gilbert, 1989;Dowsett & Livesey, 2000), defining the boundariesbetween normal and clinically significant inatten-tion, hyperactivity, and impulsivity behaviors ischallenging (Kochanska, Coy, & Murray, 2001;Kochanska, Murray, & Harlan, 2000; Keenan &Wakschlag, 2002; Nigg, Goldsmith, & Sachek, 2004;Wakschlag & Keenan, 2001). Reports of the increasein the rate of stimulant prescriptions for pre-schoolers (DeBar et al., 2003; Rappley et al., 2002;Zito et al., 2000) over the past decade have raised theconcern that normal preschool behaviors and capa-cities are being inappropriately pathologized.

Table 3 summarizes the prevalence rates for the18 DSM-IV-TR ADHD symptoms from four studies ofpreschoolers in either primary care or daycare/pre-school settings (Egger et al., submitted-b; Gadow &Sprafkin, 1997; Gimpel & Kuhn, 2000; Pavuluri,Luk, & McGee, 1999), with those symptomsendorsed for 10% or more of the children bolded.These data show (1) variation in rates by symptomswith thehyperactivity/impulsivity symptomsappear-ing to be relatively more common than the inattent-ive symptoms and (2) variation in rates by type ofmeasure, with the highest rates reported in the studythat used a ‘yes/no’ questionnaire (Pavuluri et al.,1999). However, despite the fact that some ADHDsymptoms are commonly endorsed by parents ofpreschoolers, the mean number of hyperactive/impulsive symptoms was only 1.3 (sd 1.9) in thePTRTS and 1.2 (sd 1.6) in Gadow and colleagues’study and the mean number of inattentive symptomswas 0.6 (sd 1.5) in both of these studies (Egger et al.,submitted-b; Gadow & Sprafkin, 1997). In thePTRTS, only 2.8% of the preschoolers had the six ormore symptoms needed to meet the symptom countcriterion for inattentive ADHD and only 5.6% had sixor more hyperactive/impulsive symptoms (Eggeret al., submitted-b). Of the 5.7% of the children whohad 6 or more symptoms in either or both categories,58% met full ADHD diagnostic criteria (for an overallprevalence of 3.3%) (Egger et al., submitted-b).These data suggest that the DSM-IV-TR ADHDcriteria are far from being descriptive of ‘normative’preschool behavior.

Numerous studies have shown that DSM-IV ADHDcriteria define a syndrome in preschoolers thatbehaves in terms of its correlates, heritability, andresponse to treatment like the disorder we arefamiliar with in older children (Connor, 2002;DeWolfe, Byrne, & Bawden, 2000; DuPaul, McGoey,Eckert, & Vanbrakle, 2001; Gadow & Nolan, 2002;Gimpel & Kuhn, 2000; Keown & Woodward, 2002;



Lahey et al., 1998; McGoey, Eckert, & DuPaul,2002; Sonuga-Barke, Dalen, Daley, & Remington,2002; Thomas & Guskin, 2001; Wilens et al.,2002a). The psychosocial impairment in relation-ships and functioning at home and at school,familiar from studies of older children with ADHD(Barkley, 1998; Barkley, Anastopoulos, Guevre-mont, & Fletcher, 1991), is already present duringthe preschool period (Egger et al., submitted-b;Gadow & Nolan, 2002; Lahey et al., 2004, 1998). InLahey and colleagues’ study of 126 preschoolerswith ADHD and 126 matched controls, the childrenwith ADHD (all sub-types) were significantlyimpaired in global functioning, as well as in specificsocial relationships, including those with parents,teachers, and peers, and in academic functioning(Lahey et al., 1998). A three-year follow-up foundthat children with preschool ADHD continued to befunctionally impaired across all settings and rela-tionships (Lahey et al., 2004). In the PTRTS, over40% of preschoolers who met criteria for ADHD hadalready been suspended from school or daycare,compared with only .5% of children without ADHD.Nearly 16% had been expelled (Egger et al., submit-ted-b). These data, as well as the similarity betweenthe prevalence rates for preschool ADHD reported inthe four non-specialty clinic studies reviewed above,and the consistency between preschool rates andthose reported for older children (Costello et al.,2005) and adults (Kessler, Chiu, Demler, & Walters,

2005b), indicate that the unmodified DSM-IV-TRcriteria are identifying a group of preschoolerswith non-normative hyperactivity, impulsivity, andinattention who have a valid disorder similar to thatseen at other stages of life.

Because studies in older children have shownsignificant familial clustering by ADHD sub-type, aswell as different genetic influences contributing toeach sub-type, it is critical that future studies ofpreschool ADHD assess the disorder using the DSM-IV sub-types (and the alternative latent class derivedsub-types proposed by Todd and colleagues (Toddet al., 2001)), rather than by the presence or absenceof ADHD overall alone (Rasmussen et al., 2002,2004; Rohde et al., 2001). Few studies have exam-ined ADHD sub-types in young children. So far itappears that hyperactive-impulsive and combinedtype ADHD are the two most common sub-types,with fewer children meeting criteria for pure in-attentive type (Egger et al., submitted-b; Gadowet al., 2001; Gimpel & Kuhn, 2000; Pineda et al.,1999). Further work is needed to determine whetherthe low rates of pure inattentive type ADHD inpreschoolers reflect true developmental differencesbetween younger and older children or limitations ofour current measures of preschool inattention. Infuture studies, it will also be important to examinesimilarities and differences in the behavioral mani-festations, neuropsychological correlates, and geno-types of preschoolers with different ADHD sub-types.

Table 3 Prevalence of ADHD symptoms in four non-specialty clinic studies of preschoolers

Study (N)PTRTS

(N ¼ 307*)Gimpel and Kuhn,

2000 (N ¼ 53)Pavuluri et al.,1999 (N ¼ 272)

Gadow andSprafkin, 1997 (N ¼ 531)

Age range 2–5 2–6 2.5–5 3–5Measure PAPA structured

interviewADHD Rating

Scale-IV checklistADH-P checklist ECI-P checklist

Symptom definition Glossary defined** ‘very much’ ‘yes’ or ‘no’ ‘often’ or‘very often’

Hyperactive/impulsive symptomsOften fidgets or squirms 4.5% 6.7% 18.4% 12.0%Often leaves seat 12.7% 2.9% 19.9% 12.0%Often runs/climbs 9.2% 4.0% 16.2%*** 12.5%Often has difficulty playing quietly 9.4% 0.9% 7.4% 6.5%Often ‘on the go’ 9.6% 6.3% 72.7% 24.0%Often talks excessively 17.0% 6.8% 64.6% 27.5%Often blurts answers 8.3% 1.2% NR 9.0%Often difficulty waiting turn 8.1% 8.0% 19.5% 8.5%Often interrupts or intrudes 46.6% 4.4% 26.3% 11.0%

Inattentive symptomsOften fails to attend to details 5.2% 0.4% NR 11.5%Often difficulty sustaining attention 7.3% 2.8% 8.5% 4.0%Often doesn’t seem to listen 3.5% 4.3% 36.9% 9.5%Often doesn’t follow instructions 14.4% 2.4% 3.7% NROften difficulty organizing tasks 3.4% 1.8% NR 5.5%Often avoids sustained mental effort 10.3% 2.4% NR 3.0%Often loses things 3.2% 0 27.9% 4.0%Often easily distracted 11.8% 4.8% 47.8% 12.0%Often forgetful 5.4% 0.4% NR 4.5%

*Weighted back to screening population of 1073; **symptom must occur in at least two activities and be, at least sometimes,uncontrollable by the child or by adult admonition; ***‘often does dangerous things’; ADH -P (Attention Deficit Hyperactivity-parentversion); ECI (Early Childhood Inventory); PAPA (Preschool Age Psychiatric Assessment); NR ¼ not reported; symptom prevalencesof 10% or more are bolded.



Disruptive behavior disorders: ODD andCD. Toddlerhood to kindergarten is the develop-mental period when key mechanisms of emotionaland behavioral control (and on the psychopatho-logical side – dysregulation) are established, inclu-ding the capacity to regulate anger, managefrustration, and inhibit verbal or physical reactionsto negative stimuli (Kochanska et al., 2001, 2000;Sroufe, 1990). Most children’s irritability, opposi-tionality, and aggression decrease from the ages of2 through 5 (Bhatia et al., 1990; Earls, 1980;MacFarlane, Allen, & Honzik, 1962, 1954; Moffittet al., 1996; Nagin & Tremblay, 1999; Pavuluri &Luk, 1996; Richman et al., 1982; Shaw, Gilliom,Ingoldsby, & Nagin, 2003; Tremblay, 2000; Tremb-lay et al., 1999). However, in a subset of children, thedegree of anger, as well as other negative affects, anddisruptive and defiant behaviors are severe, persist-ent, and associated with the development of laterdisruptive and affective psychiatric disorders (Moffittet al., 1996; Nagin & Tremblay, 1999; Shaw et al.,2003).

Developmentally modified criteria for ODD andCD. As with ADHD (and, perhaps, all of the dis-orders reviewed here), there has been considerablecontroversy about the diagnosis of ODD or CD inpreschool children (Keenan & Wakschlag, 2002),with concerns raised (1) that developmentally nor-mal aggression, non-compliance, defiance, and op-positionality will be inappropriately labeled aspathological (McClellan & Speltz, 2003), and (2) thatyoung children are not capable of engaging in thebehaviors that are described in the CD criteria(Campbell, 1995; Keenan & Wakschlag, 2000). Thelatter concern is certainly true for symptoms such astruancy and breaking curfew, but is less clear for asymptom like destruction of property that requiresthat the child’s behavior be ‘deliberate.’ A furtherconcern is (3) that manifestations of ODD/CDsymptoms in young children are not clinically orconceptually equivalent to manifestations of thesebehaviors in older children (e.g., is a preschooler’sassault of a peer with a toy or rock or pencil similarto an adolescent’s assault of a peer with a knife orfirearm?) (Keenan & Wakschlag, 2000).

Keenan and Wakschlag have proposed modifiedcriteria for CD in preschoolers which were adopted inthe RDC-PA. Changes include deletion of 4 symp-toms that are inappropriate for preschoolers(breaking and entering, breaking curfew, runs away,truancy), modification of the wording of othersymptoms to emphasize persistent patterns of be-havior and the age-specific presentation of thesebehaviors, and a decrease in the duration criterionfrom 12 to 6 months (Task Force on Research Dia-gnostic Criteria: Infancy and Preschool, 2003).Despite the exclusion of 4 symptoms, the cutpoint ofthree or more symptoms remained unchanged. Nospecific changes were recommended for ODD, except

to state that ODD symptoms must be persistent,pervasive, and severe so as to exclude transientperturbations in oppositionality or defiance (e.g.,secondary to the birth of a sibling).

Addressing the concerns about ODD/CD dia-gnoses listed above will require use of structuredassessments (parent report and observationalmeasures) that include the full range of oppositionaland conduct disordered behaviors in young childrenand clearly specify (1) how these behaviors are beingmeasured, (2) where (and how) frequency, duration,and severity cutpoints are being set and (3) howdevelopmental/age differences, gender differences,and the effects of context (particularly the parent–child relationship) and culture are being accountedfor in symptom definitions and diagnostic algo-rithms.

Despite the many unresolved questions, at thispoint, there is good evidence that ODD and CDsymptoms and diagnostic criteria identify groups ofimpaired preschoolers with clinically significant be-havior problems (Angold et al., submitted; Barkleyet al., 2002; Coy, Speltz, DeKlyen, & Jones, 2001;DeKlyen, Biernbaum, Speltz, & Greenberg, 1998;Keenan &Wakschlag, 2002; Kim-Cohen et al., 2005;Lavigne et al., 1998b, 1998c; Speltz, DeKlyen,Calderon, Greenberg, & Fisher, 1999a; Speltz,DeKlyen, & Greenberg, 1999b; Speltz, DeKlyen,Greenberg, & Dryden, 1995; Speltz, McClellan,DeKleyn, & Jones, 1999c; Speltz, Greenberg, &Deklyen, 1990; Wakschlag & Keenan, 2001). So fewstudies have examined ODD and CD separately thatit is not yet clear that they should be considered twoseparate disorders or a single continuous entity.Data from the non-specialty clinic studies show afairly wide range of prevalence estimates for ODD(4–16.8%) and CD (0–6.6%). Preschool ODD hasbeen found to show substantial stability or predic-tion to other disruptive behavior disorders (50–76% –as high as in older children and adolescents) over a2-year period (see also Barkley et al., 2002; Lavigneet al., 1998b, 1998c; Speltz et al., 1999c). A recentpaper by Kim-Cohen and colleagues (Kim-Cohenet al., 2005) reporting rates and concurrent, con-vergent, and predictive validity of DSM-IV CD in arepresentative birth cohort (N ¼ 2,232) of 4½–5-year-old twins provides compelling support for thediagnosis of CD, at least in older preschoolers. Theoverall prevalence was 6.6% with 2.5% of the chil-dren having moderate to severe CD, with rates inboys 3–5 times greater than in girls. Half of thechildren with CD at age 5 also met criteria at age 7.The children who no longer met CD criteria at age 7were significantly more impaired with increasedrates of educational difficulties than children whonever met criteria for CD. Sadly, this study did notassess ODD. Future studies should assess ODD andCD separately to test whether children with eachdisorder have different patterns of correlated char-acteristics and distinct outcomes.



Emotional disorders

Depressive disorders

Kashani’s early studies of preschoolers conducted inboth clinical and community settings (Kashani, Allan,Beck, Bledsoe, & Reid, 1997; Kashani & Carlson,1987; Kashani, Holcomb, & Orvaschel, 1986; Kash-ani, Ray, & Carlson, 1984) provided the first indica-tion that DSM-like depressive symptoms anddisorders could be identified in preschool children.The rate of major depressive disorder in preschoolersreported in non-clinical studies ranges from 0 to 2%(Angold et al., submitted; Earls, 1982a; Kashaniet al., 1986; Keenan et al., 1997; Lavigne et al.,1996). The studies using DSM-III criteria andunstructured assessments reported the lowest rates.The PTRTS is the only non-clinical study to reportrates of specific depressive disorders in preschoolers:1.4% with major depressive disorder, .6% with dys-thymicdisorder, and .7%withdepressionNOS/minordepression (3 rather than 5 depressive symptoms).Major depression was significantly more commonin older preschoolers than toddlers (3.0% vs. .3%;OR ¼ 12 (1.5, 101); p ¼ .02). As with prepubertaldepression, there was no difference in rates betweenboys andgirls. In the PTRTS, 93%of preschoolerswhomet the diagnostic criteria for a depressive disorderwere impaired with a mean impairment score of 12(range 0–30) (Angold et al., submitted), suggestingthat the current DSM-IV criteria are identifying aclinically significant group of children.

Luby and colleagues have conducted the mostextensive recent research on preschool depressionwith their study of 174 three- to five-year-old chil-dren, 55 of whom met criteria for depression.Prominent symptoms included sad or irritable mood,anhedonia, low energy, eating and sleeping prob-lems, and low self-esteem. From these data Luby hasproposed developmental modification of DSM-IVsymptoms, including reduction in the requirementfor persistence of depressed or irritable mood. An-other modification was that persistent death andsuicide themes in play were included in the assess-ment of suicidal ideation (Luby et al., 2002). Thesemodified criteria are included in the RDC-PA and inthe DC: 0–3R.

Luby’s study has identified characteristics andpatterns of risk similar to those reported for de-pressed older children (Goodyer, 1990; Goodyer,Herbert, Tamplin, Secher, & Pearson, 1997; Good-yer, 1995; Goodyer, Herbert, Tamplin, & Altham,2000), including denser family histories of psycho-pathology, in general, and anxiety and depressivedisorders, in particular, stability over 6 months, lowsocialization scores, higher child self-reports ofdepressive themes, and increased cortisol reactivityin response to stress, particularly in those withanhedonia (Luby et al., 2003a, 2003b, 2003c).

Because there are so few studies of preschooldepression, it is too early to determine whether the

depressive symptom clusters identified in thesestudies are phenotypically similar to the depressivedisorders diagnosed later in childhood or predictdepression later in childhood. Both Luby’s depressedpreschoolers and those in the PTRTS had very highrates of comorbidity (Angold et al., submitted; Lubyet al., 2003c), much higher than expected fromstudies of older children and adolescents (Angold,Costello, & Erkanli, 1999a). In both studies the ratesof comorbidity with ODD were substantially higherthan with anxiety disorders. These preliminary datalead one to question whether these depressive syn-dromes really do constitute valid separate disordersor whether these symptom patterns are indexing amore global emotional and behavioral dysregulationsyndrome. We discuss this further in the section oncomorbidity.

Mania and bipolar disorder

Only a handful of case studies and studies of smallsample size have examined mania and the diagnosisof bipolar disorder in preschoolers. In all of thesestudies, irritable mood, elation, decreased need forsleep, ADHD symptoms, family history of affectivedisorder and impaired functioning were prominentcharacteristics (e.g., Dilsaver, 2004; Luby & Mra-kotsky, 2003; Pavuluri, Janicak, & Carbray, 2002;Scheffer & Apps, 2004; Tumuluru, Weller, Fristad, &Weller, 2003). Using a modified version of the PAPAmania section with good test–retest reliability, Lubyand colleagues have identified a subset of pre-schoolers with symptoms similar to those describedin older children with bipolar disorders (Luby, 2005).Leibenluft and colleagues at NIMH have begun astudy of preschoolers of parents with bipolar disorderwhich will use the PAPA, including the Luby modifiedmania section, as well as other measures to examinethe symptoms of the narrow bipolar phenotype andthe broader phenotype of severe emotional dysregu-lation (Leibenluft, James, Blair, Charney, & Pine,2003) in these high risk preschoolers. At this pointthe data on preschool bipolar disorder are scarce andare far from providing evidence that bipolar disorderis a valid preschool psychiatric diagnosis.

Anxiety disorders

Remarkably little clinical or epidemiologic researchhas examined the nosology, prevalence or charac-teristics of clinically significant anxiety symptomsand disorders in preschool children. As with ADHDand ODD symptoms, a first question is whether theDSM-IV anxiety symptoms seem to be indexingproblematic behavior or common, seemingly norma-tive behavior. Our approach to developing the PAPAdiagnostic algorithm for SAD illustrates one (albeitpreliminary) approach to this question. In the PTRTS,SAD criterial symptoms ranged from being common(e.g., a quarter of preschoolers were reluctant to sleep



without being near caregiver) to very uncommon (e.g.,less than a half a percent worried about calamitousseparation from their parent) (Egger, Erkanli, Keeler,Potts, & Angold, submitted-a). Each of the SADsymptoms, except avoids being alone and separation

nightmares, was significantly associated with im-pairment. To meet DSM criteria for SAD, a child musthave 3 or more SAD symptoms that have lasted for4 weeks or more. The symptoms must also causedistress or impairment. Thus, a straight implemen-tation of the DSM SAD criteria would not requireimpairment for a diagnosis (as is true for the CAPASAD diagnostic algorithm). The overall rate of SADwithout the requirement of an impairment criteriawas 8.6% (mean impairment scale score of 6.1),dropping to 2.4% when impairment was required(mean impairment scale score of 13.6). Based onthese data, we decided to require impairment for adiagnosis of SAD in the PAPA. Similar decisions forthe diagnosis of specific phobias and social phobiawere made based on the argument that inclusion ofan impairment criterion would decrease the chancethat the diagnosis was identifying either normativeseparation or stranger anxiety or fears. Because thesymptoms of GAD and PTSD cannot be conceptual-ized as developmentally normative, we strictlyimplemented the DSM (or, in the case of PTSD, RDC-PA criteria, based on Scheeringa and colleagues’work on PTSD in preschoolers) and did not requireimpairment. We are well aware that future studiesmay demonstrate that these are not the best ways todefine preschool anxiety disorders. Diagnostic algo-rithms will need to be revisited and perhaps revisedas new data (particularly from multiple sources) areobtained.

Two recent community studies using checklistmeasures reflective of DSM criteria for specificanxiety disorders have provided support for the ideathat, already in the preschool period, clinically sig-nificant anxiety can be sub-typed in patterns similarto those identified for older children (e.g., March,Parker, Sullivan, Stallings, & Conners, 1997; Muris,Mayer, Bartelds, Tierney, & Bogie, 2001; Spence,1997). Spence and colleagues (Spence et al., 2001)assessed anxiety in 755 preschoolers using maternalreports on the 28-item Preschool Anxiety Scale(PAS). A confirmatory factor analysis found thatpreschool anxiety symptoms clustered into fivefactors that resembled the DSM-IV categories ofseparation anxiety, social phobia, obsessive com-pulsive disorder, generalized anxiety disorder, andspecific phobias (here limited to the specific fear ofphysical injury), suggesting differentiation of anxietyin early childhood. While social phobia, obsessivecompulsive disorder and fear of physical injuryappeared to be separate dimensions, separationanxiety and generalized anxiety were not as wellseparated. A study of 4,564 four-year-old twins (Eleyet al., 2003) provides similar evidence for phenotypicand genetic differentiation between specific categ-

ories of anxious behavior in young children. A con-firmatory factor analysis of a 16-item anxiety surveywhich included anxiety-related items from psychi-atric and temperament checklists identified fivefactors very similar to ones identified by Spence andcolleagues: general distress, separation anxiety,fear, obsessive compulsive behaviors, and shyness/inhibition. The correlations between the generaldistress, separation anxiety, and fear factors and theshyness/inhibition factor were quite low (.17 to .28),suggesting that anxiety symptoms were distinct frombehaviorally inhibited temperament.

As previously noted, the rates of anxiety disordersvaried considerably in the community studies ofpreschoolers, with measurement limitation, sampleselection bias, and/or lack of agreement about theboundaries between normative and clinically signi-ficant anxiety symptoms all potential reasons for thisdisparity. The PTRTS is the only diagnostic study ina non-specialty clinic sample to report rates of thefull range of specific anxiety disorders, except OCD(see Table 1). There were no significant gender dif-ferences for anxiety disorders overall or for specificanxiety disorders. Older children (4 and 5 vs. 2 and3) were more likely to meet criteria for PTSD (OR ¼2.5 (1.1, 5.8); p ¼ .03). Although the specific anxietydisorders were strongly inter-related, the patterns ofassociation of individual anxiety disorders with non-anxiety diagnoses showed some specificity. All of theanxiety disorders were bivariately associated withCD, ODD and depression, but in models controllingfor comorbidity between disorders, specific phobias,PTSD, and selective mutism were associated withdepression, while SAD and GAD remained signifi-cantly associated with ODD. Children with anxietydisorders were significantly more likely to be im-paired than children without an anxiety disorder(OR ¼ 9.3 (4.2, 21); p < .0001). On an impairmentscale (range 0–30), the mean scores for individualanxiety diagnoses were 13.7 for SAD, 7.7 for GAD,10.9 for social phobia, 12.4 for specific phobia, 8.4for selective mutism, and 14.3 for PTSD (Angoldet al., submitted).

These data suggest that (1) anxiety disorders arecommon in preschool children, (2) they exhibit sub-stantial homotypic and heterotypic comorbidity, (3)there are differences in the rates of homotypic andheterotypic comorbidity among the specific anxietydisorders, and (4) preschoolers who meet the DSMdiagnostic criteria for specific anxiety disorders aresignificantly more impaired than children without ananxiety disorder. However, little of this data has beenreplicated. Anxiety disorders need to be a priorityarea for future work on preschool psychopathology.

Diagnostic comorbidity

A number of review articles (Abikoff & Klein, 1992;Achenbach, 1990; Achenbach, 1995; Angold &



Costello, 1993; Angold et al., 1999a; Caron & Rutter,1991; Hinshaw, Lahey, & Hart, 1993; Kendall,Kortlander, Chansky, & Brady, 1992; Klein & Riso,1993; Loeber & Keenan, 1994; Nottelmann & Jen-sen, 1995; Rutter, 1997) have demonstrated theimportance of comorbidity for understanding theetiology, course, and treatment of psychiatric dis-orders. In adults and older children, comorbidity iscommon. Comorbid disorders are associated withgreater impairment than non-comorbid disorders(Angold et al., 1999a; Kessler et al., 2005b). A 1999review of the prevalence, causes, and effects of co-morbidity among child and adolescent disordersdemonstrated that comorbidity is not simply anartifact either of measurement or of nosology. It alsohighlighted the limitations of clinical samples forproviding unbiased estimates of the prevalence ofcomorbidity or rates of co-occurrence between spe-cific disorders (Angold et al., 1999a). These studiesin adults and older children have shown that wemust examine the comorbidity between specific dis-orders, not just broad internalizing and externalizingcategories, if we want to understand the etiologicalmechanisms and clinical implications of psychiatriccomorbidity (Angold et al., 1999a).

Comorbidity in preschool psychopathology

Until recently, with the development of reliablestructured assessments of the full range of psychi-atric disorders in young children, data on comor-bidity in preschool children were limited toco-occurrence between the broad categories of emo-tional and behavioral disorders (Keenan et al., 1997;Lavigne et al., 1996). In the Keenan study, a quarterof children with an emotional disorder also met cri-teria for a behavioral disorder, with the same pro-portion of children with a behavioral disorder havingan emotional disorder. In Lavigne and colleagues’study, 5.4% of the children (25.2% of children with atleast one psychiatric disorder) had comorbid dis-orders, defined as ‘a disruptive disorder comorbidwith an emotional disorder or other disorder’(Lavigne et al., 1996). In the PTRTS, comorbidity wasexamined among these five categories of disorder(s):any depressive disorder, any anxiety disorder, ODD,CD, or ADHD; 51.6% of preschoolers with at leastone disorder met criteria for a single type of disorder,25.8% had two types of disorders, and 22.6% hadthree or more types of disorder. Eight percent of thepreschoolers in the sample met criteria for more thanone psychiatric disorder. The risk of having comor-bid psychiatric disorders increased 1.6 times witheach additional year from age 2 through age 5 (OR ¼1.6 (1.1, 2.5); p ¼ .03); 18.2% of 2 and 3-year-oldswith a psychiatric disorder had more than one dis-order, compared with 49.7% of 4- and 5-year-oldswith at least one psychiatric disorder. Preschoolerswith comorbid disorders were significantly moreimpaired than preschoolers with only one disorder

(OR ¼ 20 (2.5, 165); p ¼ .005); mean impairmentscore 15.4 vs. 6.8) (Angold et al., submitted).

In the PTRTS all of the pair-wise associations be-tween these five disorders were significant, except forthat between ADHD and anxiety disorders. However,the pattern of comorbidity illustrated in Figure 2 wasfound when the effects of each disorder on all theother disorders were controlled for simultaneously.This approach accounts for what Angold has called‘epiphenomenal comorbidity’ in which apparentpair-wise associations between disorders are actu-ally a reflection of comorbidity between two otherdisorders (Angold et al., 1999a). Thus, referring toFigure 2, a preschooler with an anxiety disorder, butnot ODD, is no more likely than a child without adisorder to have CD. What is striking about thecomorbidity pattern depicted in Figure 2 is thecentrality of ODD in mediating the relationshipsbetween anxiety disorders and depression, depres-sion and CD, and the emotional disorders andADHD. A similar (but not identical) pattern ofcomorbidity has been found in two large represen-tative community studies of older children (Angoldet al., 1999a; Ford, Goodman, & Meltzer, 2003).What is significant is that each of these three studiesshows a strong relationship between depression andeither CD or ODD that mediates the relationship ofdepression with ADHD. In the preschool model, ODDalso mediates the relationship between depressionand anxiety. This pattern of comorbidity betweendepression, anxiety disorders, and ODD raises thequestion whether preschool depressive disorders aretruly equivalent to depressive disorders later inchildhood and adulthood.

Comorbidity seems to be a central feature of psy-chiatric disorders in preschoolers, as it is in olderchildren and adults. Just as capacities to regulateemotions and behaviors develop during the pre-school period, so do dysfunctions in multiple sys-tems. With the advances in our understanding of thegenetics and neurobiology of psychiatric disorder itis increasingly clear that the psychiatric ‘syndromes’

ODD AnyAnx

ADHDDEP CD

OR=4.4

OR=26

OR=26OR=347

Figure 2 Comorbidity between disorders in preschoo-lers, controlling for all of the disorders simultaneously.Non-significant ORs are not shown; OR ¼ odds ratio.



specified in the DSM are phenotypes that reflectproblems in multiple functional systems (e.g., affectregulation; behavioral regulation; attention regula-tion; regulation of serotonin; regulation of geneexpression) (Charney, Barlow, & Botteron, 2002).Many of these dimensions (for example, sleep andappetite disturbances, disturbances of motor activ-ity, or irritability) are common to multiple disorderswith seemingly different etiologies. Different co-morbidity; patterns (including lack of comorbidity,‘pure’ disorders) may be associated with differentsequences of dysfunction in underlying develop-mental processes (e.g., affect regulation, attentionregulation, inhibitory control, language develop-ment). These different comorbidity patterns may alsolead to the identification of more biologically andclinically valid sub-types of existing disorders or todefinition of new disorders (e.g., irritable depressionversus non-irritable depression) (Insel & Fenton,2005).

To advance our knowledge of preschool psycho-pathology (and later disorders), longitudinal, com-munity studies of preschoolers need to documentrates of comorbidity, but they also must move be-yond description to examine the specific and sharedenvironmental, physiological, neural, and geneticcorrelates of different patterns of comorbidity, andthe course of comorbidity from the preschool age toadulthood. Here we see an opportunity to integratethe multiple approaches and conceptualizations(temperament/emotion regulation/dimension/cate-gorical) of preschool behavioral and emotional dys-regulation and move beyond the DSM to characterizephenotypes that link genes with the brain and withbehavior (Charney et al., 2002; Nelson et al., 2002).To do this, future studies of the onset, course, andetiology of comorbidity must start no later than age2, and all studies of preschool psychopathology mustaccount for comorbidity. These data will inform ourunderstanding of the etiology, development, andpersistence of psychopathology, and will translatedirectly into clinical opportunities for targetedtreatment, early intervention and prevention withyoung children.

Limitations

In this review, we have attempted to identify themany limitations of our current conceptualization,definition, measurement, and study of behavioraland emotional disorders in preschool children. Theseinclude: (1) the lack of conceptual integration be-tween diverse approaches to normal and abnormalbehavior and affect in young children; (2) the relianceon parent report in most of the current non-clinicalstudies and the lack of a consensus about how tocombine information from multiple informants andmultiple modes of assessment; (3) the paucity of dataon the cross-sectional and longitudinal associations

between specific psychiatric syndromes and lan-guage development and capacities, cognitive func-tioning, attention regulation, impulse control, andaffect regulation and the association of specificdevelopmental disorders with psychiatric disorders;(4) the limitations of current conceptualization andmeasurement of impairment in young children; (5)the lack of research on putative risk factors associ-ated with specific preschool psychiatric disordersincluding socioeconomic and cultural factors, acuteand chronic adverse life events, disturbances in theparent–child relationship, family history of psychi-atric disorders and impairment, physical health,prenatal and perinatal factors (e.g., low birth weight,maternal smoking during pregnancy) and neurode-velopmental functioning; (6) the overall small num-ber of studies and research programs examiningpsychiatric symptoms and disorders in this agegroup; and (7) the lack of replicated findings.

Conclusion

This review highlights how early we are in the pro-cess of characterizing the nosology and epidemiologyof preschool behavioral and emotional disorders,particularly depression and anxiety disorders. How-ever, it also reveals how late we are in recognizing thedistress and impairment of preschool children andtheir families. The furor over prescription of psy-chotropic medication for very young childrenbrought to attention the lack of consensus abouthow to define and diagnose psychiatric disorders inpreschoolers and the paucity of treatment studies.However, it seems ironic that it did not lead to theconclusion that these increasing prescription ratesreflect real unmet need. In fact, very few preschoo-lers who meet criteria for a psychiatric disorder arereferred for a mental health evaluation or receivetreatment. In the Lavigne study, only 25% of presc-hoolers with a DSM-III-R disorder had been referredfor treatment (Lavigne et al., 1998a). In the PTRTS,only 11% of children who had any psychiatric dis-order had been referred for a mental health evalua-tion. While greater understanding of thepresentation, nosology, and epidemiology of pre-school psychiatric disorders will have enormousimplications for research on the causes and out-comes of psychiatric disorders, these advances arealso urgently needed so that we develop and dis-seminate clinically relevant assessment tools andevidence-based treatments, which will enablepediatricians and mental health providers to identifyand help these preschoolers and their families.

Correspondence to

Helen Egger, Center for Developmental Epidemio-logy, DUMC Box 3454, Durham, NC 27710, USA;



Tel: 919-687-4686 (x228); Fax: 919-687-4737;Email: [email protected]

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Manuscript accepted 9 November 2005



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Common emotional and behavioral disorders in preschool children