PUBLISHED VERSION

Hay, P. J. ; Fairburn, C. G.; Doll, H. A. The classification of bulimic eating disorders: a community-based cluster analysis study,Psychological Medicine, 1996; 26(4):801-812.

Copyright © 1996 Cambridge University Press

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Psychological Medicine, 1996, 26, 801-812. Copyright © 1996 Cambridge University Press

The classification of bulimic eating disorders:a community-based cluster analysis study

P. J. HAY,1 C. G. FAIRBURN AND H. A. DOLLFrom the Department of Psychiatry, University of Oxford

SYNOPSIS There is controversy over how best to classify eating disorders in which there isrecurrent binge eating. Many patients with recurrent binge eating do not meet diagnostic criteria foreither of the two established eating disorders, anorexia nervosa or bulimia nervosa. The presentstudy was designed to derive an empirically based, and clinically meaningful, diagnostic scheme byidentifying subgroups from among those with recurrent binge eating, testing the validity of thesesubgroups and comparing their predictive validity with that of the DSM-IV scheme.

A general population sample of 250 young women with recurrent binge eating was recruited usinga two-stage design. Four subgroups among the sample were identified using a Ward's clusteranalysis. The first subgroup had either objective or subjective bulimic episodes and vomiting orlaxative misuse; the second had objective bulimic episodes and low levels of vomiting or laxativemisuse; the third had subjective bulimic episodes and low levels of vomiting or laxative misuse; andthe fourth was heterogeneous in character. This cluster solution was robust to replication. It hadgood descriptive and predictive validity and partial construct validity.

The results support the concept of bulimia nervosa and its division into purging and non-purgingsubtypes. They also suggest a possible new binge eating syndrome. Binge eating disorder, listed asan example of Eating Disorder Not Otherwise Specified within DSM-IV, did not emerge from thecluster analysis.

INTRODUCTIONUntil recently, research on eating disorders hasfocused on the two well recognized symdromes,anorexia nervosa and bulimia nervosa. Clinicalexperience, however, indicates that a substantialnumber of those who present for treatment of aneating disorder do not fulfil diagnostic criteriafor either of these disorders (Mitchell et al. 1986;Bunnell et al. 1990; Hall & Hay, 1991). Aparticularly common group are those who haverecurrent episodes of uncontrolled over-eating('binges') yet do not have bulimia nervosa(Clinton & Giant, 1992; Fichter et al. 1993).

Two sources of evidence point to the im-portance of this group. First, it is now ap-preciated that a quarter or more of those whopresent for the treatment of obesity have

' Address for correspondence: Dr Phillipa Hay, Department ofPsychiatry. University of Adelaide, Royal Adelaide Hospital, NorthTerrace, Adelaide, SA 5001, Australia.

recurrent bulimic episodes similar to those seenamong patients with bulimia nervosa (Gormallyet al. 1982; Hudson et al. 1988; de Zwaan et al.1992; Wilson et al. 1993). These patients differfrom those obese patients who do not binge: forexample, they are more dissatisfied with theirshape and weight, and they have higher levels ofgeneral psychiatric symptoms (Marcus et al.1985, 1988, 1990a; Prather& Williamson, 1988;Wadden et al. 1993; Specker et al. 1994; Telch &Agras, 1994). In addition, it has been suggestedthat they may respond less well to treatment(Keefee/a/. 1984; Marcus et al. 1990*) althoughthe evidence for a differential treatment responseis weak and some controlled studies have foundno differences between those who do and do notbinge (La Porte, 1992; Wadden et al. 1992;Yanovski, 1993).

The importance of this group is also high-lighted by research on the prevalence of bulimianervosa. Community studies have found thatthe prevalence of recurrent binge eating in the

801

802 P. J. Hay and others

absence of bulimia nervosa may be as high as theprevalence of bulimia nervosa itself (Beglin,1990; Bruce & Agras, 1992; Spitzer et al. 1992a).

On these grounds it was suggested by Spitzerand colleagues that a third eating disorder beincluded in DSM-IV (Spitzer et al. 1992 a, 1993).This disorder, termed 'binge eating disorder',was designed to describe those individuals withrecurrent bulimic episodes who do not meetdiagnostic criteria for anorexia nervosa orbulimia nervosa. The suggestion attracted criti-cism on a number of grounds, the main onebeing that it was premature to demarcate thisparticular group from among all those whobinge eat, given the absence of good descriptiveand therapeutic studies on the entire population(Fairburn et al. 1993). It was eventually decidednot to include binge eating disorder as a newdiagnosis in DSM-IV. Instead, it was listed as anexample of Eating Disorder Not OtherwiseSpecified with reference to patients who haverecurrent episodes of binge eating (as defined inthe DSM-IV) in the absence of the regular use ofinappropriate compensatory behaviours charac-teristic of bulimia nervosa. Suggested specificcriteria were included in Appendix B reservedfor categories meriting further study (AmericanPsychiatric Association, 1994, p. 550 and p.729).

The aim of the present study was to derive anempirically-based scheme for classifying thosewith recurrent binge eating and to compare thepredictive validity of this scheme with that of theDSM-IV scheme. Two aspects of the method areof particular note. First, the sample wascommunity-based and designed to be composedof a broad range of those who binge eat,including those with bulimia nervosa; andsecondly, the subjects were assessed using astandardized investigator-based interview.

METHODDesignA representative community-based sample ofyoung women with recurrent binge eating wasrecruited. To identify subgroups among thesample it was subjected to a cluster analysisbased on current eating disorder features. Thedescriptive and construct validity of the clustersolution was evaluated. The sample was followed

up 1 year later to test the predictive validity ofthe cluster solution, and to compare its predictivevalidity with that of the DSM-IV scheme(American Psychiatric Association, 1994).

Subjects and definitions

The aim was to recruit a broad sample of thosewith recurrent binge eating. There has beenconsiderable uncertainty over how best to definea binge (Fairburn & Wilson, 1993). There isconsensus among technical and lay definitionsthat there should be a sense of loss of control(Beglin & Fairburn, 1992 a), but there is lessagreement over whether the amount eatenshould also be large (Fairburn et al. 1986;Garner et al. 1991). For the purpose of thisstudy, binge eating was defined as an episode ofeating that was associated with a sense of loss ofcontrol at the time and that was viewed by thesubject as large (i.e. the definition included both'subjective' and 'objective' bulimic episodes-see Assessment below). This choice of definitionallowed us to investigate subjects with bulimicepisodes of varying size. Objective bulimicepisodes accord with the definition of a binge inDSM-IV (American Psychiatric Association,1994). 'Recurrent' was defined as having had atleast 12 bulimic episodes (as defined above) overthe previous 3 months. While the DSM-III-Rand DSM-IV definitions of bulimia nervosarequire binges to occur on average at least twicethis rate, there are no data which support thisspecific threshold. Indeed, there is evidence thatthose who binge on average once a week do notdiffer from those who binge more often withrespect to their specific eating disorder features,general psychopathology and outcome (Wilson& Eldredge, 1991). The study was confined towomen aged between 16 and 35 years, since thisis the group among whom eating disorders, suchas bulimia nervosa and anorexia nervosa, appearto be most common. Subjects were excluded ifthey were pregnant, or had medical problems ortreatments that were likely to affect their eatingor weight.

Recruitment and follow-up procedure

The subjects were recruited from women aged16 to 35 years whose names were listed on thecase registers of 19 general practices located inurban and rural areas of Oxfordshire. Thismode of recruitment is a good way of obtaining

Classification of bulimic eating disorders 803

a local general population sample since prac-tically all of the British population is registeredwith a general practitioner (Office of HealthEconomics, 1987). These women were sent aself-report questionnaire (Fairburn & Beglin,1995) (see below) designed to identify eatingdisorder features. Subjects who did not returnthe questionnaire were sent a second one.Respondents who reported recurrent episodes ofover-eating were invited to be interviewed.Identifying the response rate in a study of thistype is difficult since general practitioner registersare invariably overinclusive (i.e. they include thenames of people who have subsequently movedaway from the area). It is, therefore, not possibleto conclude that non-response is indicative ofthe subject having received the questionnaireand chosen not to take part. For this reason adetailed pilot study was undertaken to evaluatethis method of recruitment (Beglin, 1990). Itinvolved attempting to trace all non-respondentsto determine who had moved away from thearea. Once their absence had been taken intoaccount, the response rate was found to be 86%.The subjects were re-interviewed 1 year later toassess change in their eating disorder features.

Assessment of eating disorder features

The eleventh edition of the Eating DisorderExamination (EDE; Cooper & Fairburn, 1987;Fairburn & Cooper, 1993) was used to measurethe behaviour and attitudes characteristic ofthose with eating disorders. The EDE is aninvestigator-based interview that assesses boththe frequency of key behaviours (e.g. variousforms of over-eating, self-induced vomiting,laxative and diuretic misuse) and the severity ofother important aspects of the characteristicpsychopathology of eating disorders. Five sub-scales may be derived from its ratings (Restraint,Shape Concern, Weight Concern, Bulimia andEating Concern). The overall severity of eatingdisorder psychopathology may be quantifiedusing the global EDE score (the mean of the fiveEDE subscale scores (Fairburn & Cooper,1993)). Tests of the reliability and validity of theEDE support its use (Cooper et al. 1989; Wilson& Smith, 1989; Rosen et al. 1990; Beumont etal. 1993).

The EDE distinguishes four forms of over-eating; objective bulimic episodes, subjectivebulimic episodes, episodes of objective over-

eating and episodes of subjective over-eating.These are mutually exclusive, although it is notuncommon for subjects to have episodes ofmore than one type. The distinction between thefour types is based upon the presence or absenceof two features, loss of control during theepisode (required for both types of bulimicepisode) and the consumption of an objectivelylarge amount of food (required for objectivebulimic episodes and episodes of objective over-eating). 'Loss of control' is rated as present ifthe subject would have had difficulty eitherpreventing the episode from starting or stoppingonce it had started. The amount eaten is classedas 'large' when it clearly exceeds the quantitythat would usually be eaten under the cir-cumstances. This decision is made by theinterviewer following specific guidelines.

Fully operational eating disorder diagnosesmay be derived on the basis of EDE ratings.Specific definitions have been devised for theDSM-IV concepts of anorexia nervosa, bulimianervosa and binge eating disorder (Fairburn &Cooper, 1993). For the purposes of this studybulimia nervosa was divided into two subtypes:a purging type in which the 'purging' (vomitingor the misuse of laxatives or diuretics) occurredon average at least once weekly for 3 monthsand a non-purging type in which purging did notoccur at all. Fourteen subjects with episodes ofpurging that occurred less than weekly wereexcluded from the analyses relevant to theevaluation of the DSM-IV scheme (but not thecluster analyses) since their status in this schemeis unclear. An operational definition of eatingdisorder not otherwise specified (EDNOS) wasalso devised which was designed to identifythose who were likely to have a clinicallysignificant disturbance of eating.

The self-report case-finding questionnaire (theEating Disorder Examination-Questionnaireversion or EDE-Q) was derived from the EDE.It has been validated against the EDE and hasbeen shown to provide a good measure of manyeating disorder features (Fairburn & Beglin,1995). With respect to its assessment of bingeeating, it is overinclusive and, as a result, theEDE-Q is vulnerable to generating false positivecases (Beglin & Fairburn, 19926). This may be alimitation inherent to self-report questionnairesin general rather than being specific to thisparticular instrument (Wilson, 1993).

804 P. J. Hay and others

Assessment of other featuresGeneral psychiatric symptoms were measuredusing the Brief Symptom Inventory (Derogatis& Melisaratos, 1983). Social functioning wasassessed using the British adaptation of theSocial Adjustment Scale (Cooper et al. 1992).Self-esteem was assessed with the Robson 12-item questionnaire (Robson, 1989). Parentaland personal histories of obesity were obtainedby interview. Parental obesity was regarded aspresent when subjects reported that theirparent's highest ever weight was equivalent to abody mass index of 30 or more. Personal obesitywas rated as present when they providedconvincing evidence of having been significantlyoverweight prior to the onset of any sustaineddisturbance in eating (for example, such thatthey could not take part in sport, or such that adoctor had advised them to lose weight).Histories of psychiatric disorder were obtainedusing the Structured Clinical Interview for DSM-III-R (SCID; Spitzer et al. 19926) and theFamily History Research Diagnostic Criteria(Endicott et al. 1978).

EthicsThe study was approved by the PsychiatricResearch Ethics Committee of OxfordshireRegional Health Authority.

Statistical analyses

The first step of the cluster analysis was aprincipal components analysis for the purposeof reducing the dimensionality of the data(Everitt & Dunn, 1991). The second step was aWard's cluster analysis (Ward, 1963; StatisticalAnalysis System (SAS) Release 6.07, 1989). Acombination of clinical judgement, subjectiveinspection of the dendrogram structure, and theresults of the pseudo-F statistic, the pseudo-?2

statistic and Cubic Clustering Criterion (CCC)were used to choose the optimal cluster solution.In addition, a general rule was applied that ameaningful cluster should consist of at least 10subjects (Cyr et al. 1986; Welch et al. 1990). Thethird step involved evaluating the robustness ofthe Ward's solution by performing two furthercluster analyses: a Ward's analysis repeated ona 75% random sample and a hierarchicalcomplete linkage cluster analysis (SAS, 1989).The unweighted Kappa coefficient (Everitt,

1989) was used to assess the reliability of thecluster solutions.

The x2 t e s t a nd analyses of variance withTukey's multiple comparison procedure, asappropriate, were used to test for differencesbetween clusters and between the DSM-IVdiagnostic groups. Because this involved mul-tiple testing across the same subjects, onlysignificance levels which reached P<00\ arereported. Prior to the analysis of variance,variables that were not normally distributedwere transformed to rank normal.

Univariate tests of construct validity werecarried out using variables external to theclustering solution. A non-parametric dis-criminant function analysis, the ^-nearest neigh-bour method (SAS, 1989), was also performed.Its purpose was to test the validity of distin-guishing between clusters on the basis of featuresexternal to the cluster analysis, when thesefeatures were examined from a multivariaterather than a univariate point of view.

The relative predictive validities of the originalcluster solution and the DSM-IV scheme wereevaluated by canonical discriminant functionanalyses (Grayson et al. 1990). This techniqueidentifies linear combinations of quantitative(explanatory) variables that summarize best thedifferences between groups. The changes in thefive EDE subscale scores over the year of follow-up were entered as the explanatory variables.The eigenvalues and F-statistic results werecompared for each diagnostic scheme to assesswhich had the better predictive validity.

RESULTSThe sampleSeven hundred and fifty-five subjects wereselected for interview on the basis of theirresponses of the EDE-Q. Of these, 142 (19%)could not subsequently be traced, and 76 (10%)declined to take part. The remaining 537 (71 %)subjects completed the recruitment interview. Ofthese, 255 (47%) did not meet the inclusioncriteria for this study (i.e. they were falsepositives) and 21 (4 %) met the exclusion criteria,the most common reason being pregnancy. Ofthe remaining 261 subjects, 11 (4%) wereexcluded because of uncertainty over the exactfrequency of their episodes of overeating or

Classification of bulimic eating disorders 805

Table 1. The eating disorder features of the subjects in the four Ward clusters

Objective bulimic episodesfMedianMeanS.D.

Subjective bulimic episodesfMedianMeanS.D.

Self-induced vomitingfMedianMeanS.D.

Laxative or diuretic misusefMedianMeanS.D.

Shape concern}MeanS.D.

Weight concern}MeanS.D.

Restraint}MeanS.D.

Global EDE score}MeanS.D.

Cluster 1(N = 30)

28-543-846-9

14-519-923-3

76089-574-4

22-053-672-4

3-81-4

3-91-4

3-71-1

3-20-8

Cluster 2(N = 86)

27-029-3180

0-09-6

17-9

0010-424-5

007-6

14 6

3-711

3-41-2

3-41-0

3-10-7

Cluster 3(N = 30)

009-6

17-2

117-5119-448-2

0-01-64-6

0017138-9

3-411

301-3

2-51-3

2-70-8

Cluster 4(N= 102)

8011-714-6

13016-316-2

002-79-8

00204-9

2-71-1

2-510

2-01-3

200-7

F*

2608

72-21

61-37

14-33

17-93

16-93

28-40

45-25

Tukey

1 > 4, 1 > 32 > 4, 2 > 3

1 < 3, 2 < 32 < 4, 3 > 4

1 > 4, 1 > 21 > 3, 2 > 4

1 >3 , 1 >21 >4

1 > 4, 2 > 4

1 >3 , 1 > 42 > 4

1 >3 , 1 > 42 > 3, 2 > 4

1 > 4, 2 > 43 > 4

Note: where data were highly skewed the median is presented as well as the mean.* ANOVA Fstatistic, df = 3 and P < 0001 for all tests, Tukey test P < 001.t Number of episodes over last 3 months.} EDE = Eating Disorder Examination subscale (Fairburn & Cooper, 1993).

purging behaviour. Thus, the final sample tives or diuretics. The weight distribution of theconsisted of 250 subjects with recurrent binge sample was as follows (expressed as body masseating. index (BMI; Garrow, 1988)): 16 (7%) < 200;

The mean age of the subjects was 24-7 years 126 (57%) 20-0-24-9; 46 (21 %) 25-0-29-9; 29(S.D. = 5-5). One hundred and twelve (45%) (13%) 30-0-39-9; and 5 (2%) > 400.were married or living as married, 128 (51%) Ninety-three subjects (37%) met the EDEwere single, and 10 (4%) were divorced or operational definition of bulimia nervosa; noneseparated. Their parental social class distri- met the criteria for anorexia nervosa; and 63bution was as follows (Office of Population (25 %) met the criteria for binge eating disorder.Censuses and Surveys, 1980): 100(40%) I or II; A further 60 (24%) subjects met criteria for107 (43%) III; and 43 (17%) IV or V. EDNOS but not binge eating disorder. Thirty-

By definition, all the subjects had recurrent four subjects (14%) fell below threshold criteriaepisodes of binge eating. One hundred and for EDNOS.eighty-two (73 %) had objective bulimic episodeswith a mean weekly frequency of 2-5 episodes T h e P»"cipal components analysis(S.D. 21); 149 (60%) had subjective bulimic Data on 22 EDE items were entered into theepisodes with a mean weekly frequency of 3-8 principal components analysis. These itemsepisodes (S.D. 3-9); 31 (12%) had episodes of represented a comprehensive range of eatingobjective over-eating; 88 (35%) practised self- disorder behaviours and attitudes. (Details ofinduced vomiting; and 87 (35%) misused laxa- these items are available to interested readers

806 P. J. Hay and others

upon request.) The first seven principal com-ponents which resulted were selected for use asthe variables in the cluster analyses. Each had aneigenvalue greater than 10 and together theyexplained more than 80 % of the variance.

Ward's cluster analysisThe pseudo-F statistic suggested a six- or two-cluster solution and the pseudo-/2 statisticsuggested a four- or six-cluster solution. TheCCC did not suggest any particular clusteringsolution. The six-cluster solution was evaluated.It contained two clusters that had fewer than 10subjects, one with only two subjects and onewith nine subjects. The first two subjects wereoutliers and had atypical clinical characteristicswith an unusually high frequency of episodes ofobjective over-eating and low scores on othereating disorder features. They were excludedfrom further consideration. The latter ninesubject cluster joined a cluster with 21 subjectsto form a branch of the cluster dendrogram at ahigher level. The subjects in these two clustershad similar EDE subscale scores. It was decidedto combine these two clusters thereby generatinga four-cluster solution.

Replication of Ward's cluster solutionThe replication of Ward's method on a 75 %random sample (TV =198) produced a four-cluster solution, with clusters that had verysimilar characteristics to those produced usingthe full sample. The assignment of subjects tothe original Ward cluster set was compared withthe assignment of subjects to the correspondingnew cluster sets. There was a 77% level ofagreement of subject assignment (kappa = 0-65).

The pseudo-Fstatistic for the complete linkageclustering suggested an eight-cluster solution.For this solution the three largest groups hadsimilar symptom profiles to three of the Wardclusters and, if regrouped, a further three clusterswere similar to the fourth Ward cluster. Thelevel of agreement of assignment of subjects toclusters with similar symptom profiles was 80%(kappa = 0-70).

Internal validation: descriptive validity

The eating disorder features of the four Wardclusters are shown in Table 1. In clinical termsthey may be described as follows.

Cluster 1 (N = 30)These subjects had the most severe eatingdisorder. They were characterized by having ahigh frequency of vomiting (83 % had at leastweekly episodes, only one had no vomiting) andlaxative or diuretic misuse (47% had at leastweekly episodes, 11 had none). Both objectiveand subjective bulimic episodes were common(66% had at least weekly objective bulimicepisodes, 30% had none; 50% had at leastweekly subjective bulimic episodes, 43% hadnone). Other eating disorder features, includingdietary restraint, were prominent.

Cluster 2(N= 86)These subjects had frequent objective bulimicepisodes (92 % had at least weekly episodes) butfew subjective bulimic episodes (65 % had none,and only 29% had at least weekly episodes).More than half (61 %) did not vomit (only 23%had at least weekly vomiting) and 62 % did notmisuse laxatives or diuretics (21 % had at leastweekly episodes). The levels of dietary restraintand concern about shape and weight were high.

Cluster 3(N= 30)These subjects had a high frequency of subjectivebulimic episodes, all at least weekly. In contrast,60 % had no objective bulimic episodes and only30% had at least weekly episodes. The majority(87%) did not vomit and 66% did not misuselaxatives or diuretics. Levels of dietary restraintand shape and weight concern were high.

Cluster 4 (N= 102)This group was heterogeneous. It was composedof subjects with subjective bulimic episodes(61% had at least weekly episodes, 30% hadnone) and/or objective bulimic episodes (45 %had at least weekly episodes, 37% had none).The majority (79 %) did not vomit and 77 % didnot misuse laxatives or diuretics. Other eatingdisorder features were mild in severity.

The four clusters differed significantly in theireating disorder features (see Table 1). Com-parisons between cluster 4 and clusters 1 and 2were particularly likely to reach statisticalsignificance. Clusters 1 and 2 were the mostsimilar and differed significantly only on levelsof self-induced vomiting and laxative or diureticmisuse.

Classification of bulimic eating disorders 807

Table 2. Present state and background features of subjects in the four Ward clusters

Prcscnl state featuresAge (years)Social adjustment*

Level of psychiatric symptoms"Self-esteem''Body mass index"Alcohol use (units/week)

Background featuresOnset age'Max alcohol use ever (units/week)

History of overweight'History of anorexia ncrvosaHistory of purging'Dieting before binge eating"History of depression'Family eating disorderParental obesity (BMI > 30)Family history of depression'Family alcohol/substance abuse1

Cluster 1Mean (S.D.)

24-3 (5-4)1-6 (0-5)

1-5(0-8)34-8(17-7)22-7 (2-3)

5-5 (6-7)

17-2(4-2)20-7(28-1)

N (%)

2(7)4(13)

28 (93)12(67)9(30)3(10)

13(43)8(27)8(27)

Cluster 2Mean (S.D.)

24-7 (5-4)1-4(0-5)

11 (0-9)41-5(15-4)25-7 (60)

6-6(10-4)

160(4-6)19-7(28-5)

N (%)

16(19)9(11)

55(64)33(59)22(26)15(17)33 (38)28 (33)26 (30)

Cluster 3Mean (S.D.)

25-2 (5-4)1-4(0-5)

I I (0-9)411 (16-7)26-7 (6-2)

7-6(13-3)

16-3(5-6)25-8 (28-4)

N (%)

4(13)5(17)8(27)8(57)

12(40)3(10)

11(37)8(27)

11(37)

Cluster 4Mean (S.D.)

24-6 (5-7)1-2 (0-3)

0-7 (0-6)48-5(12-3)251 (5-3)

5-8 (8-3)

17-1 (4-4)15-8(25-6)

N (%)

18(18)11(11)30 (29)25 (57)19(19)10(10)40 (46)25 (25)27(26)

N

248208

227194220248

238247

N

248248247132248248248248248

ANOVAF

2-228-94*

6-05*6-86*215015

1-020-75

/(df=3)

2-581-36

52-941 606-222-940-321-561-32

TukeyP < 001

NS1 > 4 ,2 > 41 > 41 < 4NSNS

NSNS

P

NSNS

< 0001NSNSNSNSNSNS

" Total role area score derived from the Social Adjustment Scale (Cooper et al. 1982)." General severity index (GSI) derived from the Symptom Checklist-53 (Derogatis & Melisaratos, 1983).'' Derived from Robson (1989) questionnaire.'' Body mass index = weight divided by height squared (in kg/m!),0 Onset of a sustained (at least 3 months) eating disorder feature.' Prior to the onset of a sustained eating disorder feature." Purging refers to a history of self-induced vomiting and/or laxative or diuretic misuse sustained for at least 3 months.h Having a history of restrictive dieting prior to the onset of objective bulimic episodes.' Diagnoses assessed using sections from the Structured Clinical Interview for DSM-III-R (Spitzer et al. I992A).1 Family History Research Diagnostic Criteria (Endicott et al. 1978).• /> < 0001.

External validation: construct validity

The construct validity of the four Ward clusterswas evaluated against external characteristics(i.e. those not used in the clustering solution).The results are shown in Table 2.

There were significant differences between thecluster groups in their levels of general psy-chiatric disturbance, self-esteem and social ad-justment. Those in clusters 1 and 2 were alsomore likely to have a history of laxative ordiuretic misuse. There were no significantdifferences between the groups in any of thefamily or personal history variables. There wasa trend for subjects in Cluster 1 to weigh lessthan the subjects in the other three clusters( f < 0 1 ) .

The discriminant function analysis of con-struct validity was performed on 16 of the 17variables listed on Table 2 and 158 (63%)subjects. This was because of the high number of

missing values for the variable' dieting precedingbinge eating'. In the analysis the total misclassi-fication rate of actual and predicted clustergroupings was as follows: cluster 1,0%; cluster2, 35%; cluster 3, 16%; and cluster 4, 56%.

External validation: predictive validityTwo hundred and seven (83 %) of the original250 subjects were reassessed 1 year later, 206 ofwhom were members of the Ward's clustersolution. Of the 43 subjects who did not completea follow-up assessment, 22 (9%) declined to beinterviewed, 19 (8%) could not be contactedand two (0-8%) were physically unwell. Therewere no significant differences in social class,age, age at onset of eating disorder and severityof eating disorder features between those whowere followed-up and those who were not.

The subjects who were followed up weresubdivided using two different classificatoryschemes based on their original eating disorder

808 P. J. Hay and others

Table 3. Outcome of the subjects in the four Ward cluster groups and the DSM-IV diagnosticgroups at one year

Cluster 1N = 22

Cluster 2Af=70

Cluster 3N = 29

Cluster 4/V=85

Global EDE score, mean (s.D.)Outcome category"!. N (%)

Bulimia nervosaEDNOSNon-caseRecovered

2-8(11)

10(46)8(36)3(14)1(5)

2-2(1-2)

15(21)21 (30)26(37)8(11)

1-9(1-1)

5(17)8(28)

10(35)6(21)

1-6(0-9

6(7)21 (25)39 (46)19 (22)

BN-PN = 50

DSM-IV diagnostic groups"BN-NP BED EDNOSN=\S N = 5\ N = 49

Non-case

Global EDE score, mean (s.D.)Outcome category1!}, N (%)

Bulimia nervosaEDNOSNon-caseRecovered

2-5(1-2)

20 (40)14(28)11 (22)5(10)

2-2(1-0)

2(13)7(47)5(33)1(7)

1-7(1-1)

6(12)14(28)23 (45)8(16)

20 (0-9)

5(10)16(33)20(41)8(16)

1-2(0-8)"

1(4)4(14)

14(48)10(35)

* BN-P = purging bulimia nervosa; BN-NP = non-purging bulimia nervosa; BED = binge eating disorder; EDNOS = Eating Disorder NotOtherwise Specified; non-case = subjects with recurrent binge eating falling below threshold for a disorder of clinical severity.

6 Subjects were divided into four outcome categories: bulimia nervosa (there were no subjects with anorexia nervosa); EDNOS; ' recovered'- defined as having had no objective or subjective bulimic episodes and no purging over the preceding 3 months, and having a global EDEscore within 1 s.D. of the mean of a local general population sample of women (Beglin, 1990); and ' non-case' which was an intermediate groupnot meeting criteria for the other three categories.

* Tukey statistic: 1 > 4, 2 > 4, P < 001. •* Tukey statistic: BN purging > Binge Eating Disorder and non-cases, P < 001.t / = 26-8, df = 9, /> = 0-002. f t * ' = 36-5, d f = 12,/>< 0-001.

features. The first was Ward's clustering solutionand the second was the DSM-IV scheme.Outcome was described in two ways. First, theglobal EDE score was used to provide a measureof the overall severity of eating disorder features.Secondly, subjects were divided into four out-come categories: bulimia nervosa or anorexianervosa (there were no subjects with the latterdiagnosis); EDNOS; 'recovered'-defined ashaving had no objective or subjective bulimicepisodes and no purging over the preceding 3months, and having a global EDE score within1 s.D. of the mean of a local general populationsample of women (Beglin, 1990); and anintermediate group not meeting criteria for theother three categories.

The relative outcomes of the groups derivedfrom the cluster solution are shown in Table 3.The majority of subjects (82 %) in Ward's cluster1 met criteria for an eating disorder at follow-upwhereas half (51%) in cluster 2 did so. Theproportion with bulimia nervosa in the twogroups was 40 % and 20 % respectively. Thirteen(45%) of those in cluster 3 and 27 (32%) ofthose in cluster 4 met criteria for an eatingdisorder case. The overall difference in outcome

of the four clusters was statistically significant( / = 26-8, df = 9, P = 0002). A similar patternwas seen in the global EDE scores. Those inclusters 1 and 2 had significantly higher scoresthan those in cluster 4 (ANOVA F = 10-3, df =3, P < 0001, Tukey test P < 001).

There were also significant differences inoutcome between the DSM-IV diagnosticcategories. Forty per cent of those with purgingbulimia nervosa had bulimia nervosa at follow-up. A similar proportion of those with purgingand non-purging bulimia nervosa met criteriafor an eating disorder (68% and 60% re-spectively) whereas 40 % and 43 % of the bingeeating disorder and EDNOS cases did so. Theoverall difference in outcome was statisticallysignificant (x

2 = 36-5, df = 12, P < 0001).Those in the purging bulimia nervosa group hadsignificantly higher global EDE scores at follow-up than those in the binge eating disorder andnon-case groups (ANOVA F = 7-85, df = 4,P < 0001).

The changes in the five EDE subscale scoresover the year of follow-up were entered asexplanatory variables in two canonical dis-criminant function analyses, one based on

Classification of bulimic eating disorders 809

Ward's solution and the other based on theDSM-IV scheme. The sizes of the eigenvaluesand levels of statistical significance of the F-statistic reflected the between-group differencesin symptom change. Large between-groupdifferences would support different groups fol-lowing distinct courses. The scheme with thehigher eigenvalue (0-12) and higher level ofstatistical significance (P = 0-0006) on the firstcanonical variable was Ward's cluster solution.It was therefore regarded as having the betterpredictive validity. The eigenvalue for the DSM-IV scheme was 008 (P = 0-2).

DISCUSSION

The first goal of this study was to identifyclinically meaningful subgroups among thosewith recurrent binge eating using cluster analysis.Cluster analysis is a well established andappropriate statistical technique for suggestingpossible diagnostic categories since it attemptsto divide individuals into clusters of those withsimilar features.

The present sample was of sufficient size for acluster analysis. Although not all subjects couldbe traced and 10% declined to take part, it waslikely to be reasonably representative of youngwomen with recurrent binge eating, and certainlymuch more so that clinical samples given theirvulnerability to bias (Fairburn et al. 1995). Theonly group of such young women not repre-sented in the sample was those with the bulimicform of anorexia nervosa. Such subjects areuncommon in community samples (King, 1989;Meadows et al. 1986) and are therefore difficultto recruit in large numbers. Relevant features ofthe specific psychopathology of eating disorderswere used to cluster the subjects, and externalfeatures (including outcome at 1 year) were usedto validate the cluster solution.

Ward's method produced a four-cluster sol-ution which was replicated in a random 75%sample of the subjects and partially replicatedusing another cluster analysis method. Thefirst cluster was composed of subjects with asevere eating disorder. The high frequency ofself-induced vomiting and purging was theirmost notable feature, although they also had ahigh level of dietary restraint and concern aboutshape and weight. Their clinical pictureresembled the purging form of bulimia nervosa

except that their binges were not necessarilylarge.

The subjects in the second Ward clusterresembled the first in that they also had a severeeating disorder and they had a high frequency ofobjective bulimic episodes, but fewer vomited orabused laxatives or diuretics. Many could besaid to have the 'non-purging' type of bulimianervosa in that while they did not purge theyhad high levels of dietary restraint and extremeconcerns about shape or weight. They did notresemble' binge eating disorder', as described bySpitzer and colleagues (1992a, 1993) and out-lined in the DSM-IV (American PsychiatricAssociation, 1994), in view of the severity oftheir other symptoms. In particular, unlike thosewith binge eating disorder, but like those withpurging bulimia nervosa, they had a high levelof dietary restraint, i.e. they used an'inappropriate compensatory behaviour'(American Psychiatric Association, 1994).

The most distinctive feature of the subjects inthe third cluster was a high frequency ofsubjective bulimic episodes. They did not re-semble 'binge eating disorder' as defined in theDSM-IV as their bulimic episodes were notobjectively large. At present subjects with thisconstellation of symptoms would be categorizedwithin 'Eating Disorder Not OtherwiseSpecified' in the DSM-IV scheme or AtypicalBulimia Nervosa in the ICD-10 scheme (WorldHealth Organization, 1992). Almost nothing hasbeen written on subjects of this type (Fairburn &Walsh, 1995).

The subjects in the fourth cluster were theleast disturbed and most heterogeneous group.Their bulimic episodes tended to occur in thecontext of few other features of an eatingdisorder.

The evaluation of construct validity revealedno significant differences between the clustergroups in the frequency of the family or personalhistory variables studied. This suggests thatthese factors may be general risk factors forrecurrent binge eating, rather than specific riskfactors for particular eating disorders. This,however, needs to be tested in case-controlstudies. The evaluation of construct validity did,however, find significant differences between thegroups in current levels of general psycho-pathology, self-esteem and social adjustment.Those in the first cluster had the most severe

810 P. J. Hay and others

general psychiatric symptoms, lowest self-esteemand poorest social adjustment, while those in thefourth cluster had the least severe levels ofpsychosocial disturbance. The construct validityof the first and third cluster groups wassupported by a multivariate analysis.

There was good support for the predictivevalidity of the groupings generated by the clusteranalysis since there were significant differencesbetween them at 1 year follow-up. Similarly,there was support for the predictive validity ofthe DSM-IV scheme. The predictive validity ofthe cluster solution was superior to that of theDSM-IV scheme since the change in severity ofeating disorder features on discriminant functionanalyses significantly discriminated between theWard's clusters but not between the DSM-IVdiagnostic groups.

The findings of the study have five mainimplications for the classification of those withrecurrent binge-eating. First, the study failed toprovide evidence to support the construct' bingeeating disorder' since none of the cluster groupsresembled this condition. It could be argued thatthis is because the sample was too young and didnot include enough women with moderate tosevere obesity. Studies of patients with bingeeating disorder suggest that binge eating dis-order, in contrast to bulimia nervosa, mainlyaffects women in their thirties and forties andthose who are obese (e.g. Wilson et al. 1993;Brody et al. 1994). Spitzer & colleagues (1992a)also found binge eating disorder to be commonin women attending hospital-affiliated weightcontrol programmes. However, in the non-patient community samples binge eating dis-order occurred in only 4-4% of obese (BMI >27-5) subjects and of the 19 cases, eight hadnever been obese. The findings of the presentstudy, and those of another community-basedstudy (Dansky & Brewerton 1996), suggest thatthis association, namely with obesity, may reflectreferral bias rather than true characteristics ofthe disorder. In the present study, the mean ageof those with DSM-IV binge eating disorder was25-4 years (S.D. 5-9) and 30 (48%) had a BMI of>25.

Secondly, the findings provide support for theDSM-IV practice of subtyping bulimia nervosaaccording to the presence or absence of purging,since the first two Ward clusters resembled thesetwo categories. These clusters differed from each

other mainly in terms of the severity of eatingdisorder features rather than the features them-selves. There were no differences between themwith respect to levels of general psychopath-ology, self-esteem or social adjustment. On theother hand support was provided for retainingthe distinction between them, as the two clustersdiffered in their outcome at 1 year.

The third finding is that the defining featuresof the first group (that which most closelyresembled the purging type of bulimia nervosa)did not require the episodes of binge eating to beobjectively large. This broad definition of bingeeating is in line with earlier recommendations(Fairburn et al. 1986; Garner et al. 1991), andwith the lay understanding of the term (Beglin &Fairburn, 1992 a).

The fourth finding of note is that one of theclusters (cluster 3) is not represented in currentdiagnostic systems. This cluster was charac-terized by recurrent subjective bulimic episodes,a low frequency of vomiting and intermediatelevels of dietary restraint in the presence ofmoderately high levels of general psychiatricsymptoms. This disorder was not transitory inthat almost half of the group still had an eatingdisorder 1 year later. Further research is neededon the characteristics and course of this group.

Finally, the findings are consistent with thehypothesis that bulimic eating disorders occuron a continuum, ranging from mild eatingdisorders (those with subjective bulimic episodesand a low frequency of purging behaviours)through to severe eating disorders (those withobjective bulimic episodes and purging). Thus, itcould be argued that there is a single bulimiceating disorder, rather than two or three differentbulimic eating disorders.

Before the findings of this study can be usedto justify adjusting current diagnostic practices,they will need to be replicated using a samplefrom a different population. Replication wouldprovide support for the stability of the clustersolution. Any demonstration that the clustergroups have a differential response to one ormore specific treatments would also add to theirvalidity.

Financial support for the study was provided by aprogramme grant (18157) from the Wellcome Trustsupplemented by a grant (9202) from the John D. andCatherine T. MacArthur Foundation Research

Classification of bulimic eating disorders 811

Program. Both grants were held by C.G. F., the latterobtained in collaboration with G. Terence Wilson (ofRutgers University), Judith Rodin (of Yale Uni-versity) and P.J.H. P.J.H. also received personalsupport from a Nuffield Medical Fellowship (1991—4)and a Girdler's Junior Research Fellowship to GreenCollege, Oxford (1991-3). C.G.F. is supported by aWellcome Trust Senior Lectureship (13123) whichalso provides support for H.A.D.

We are grateful to Zafra Cooper and David Garnerfor their comments on the manuscript. We are alsograteful to Faith Barbour, Jenny Burton, BeverleyDavies, Valerie Dunn, Jan Francis, Patricia Norman,Marianne O'Connor, Sue Shaw, Angela Tremayne,Sarah Welch and Valerie Williams, who assisted withrecruitment and assessment of the subjects.

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