11 epidemiology

PSYCHIATRIC EPIDEMIOLOGY

Definition

• Study of the distribution of illness in populations over time and space

• The study of ‘Mass aspects of disease’

• The pursuit of recurrent and predictable patterns of behaviour in a given population

Uses of Epidemiology

1. Completing the clinical picture

2. Community Diagnosis

3. Secular changes in incidence

4. Identification of Risk /Protective Factors/Prevention

5. Delineation of syndromes

6. Planning services

Epidemiology Terms

• Rates and Ratios

• Prevalence– Point– Period– Lifetime– Treated and untreated

• Inception (Incidence)

Prevalence and Inception Rates

• Persons » A -----------------------

» B ---------------

» C ------------

» D ------

» E

____________________________

t0 t1 t2 t3

Relative Risk/Odds Ratio

• Attributable Risk = difference between 2 incidence rates ( exposed-not exposed)

• Relative risk = ratio of incidence rates of exposed and non-exposed

• Odds Ratio= ratio of odds of exposure of case patients to odds of control subjects ( not exposed)

Odds ratio

• Odds RatioA= 30 B = 60

C= 10 D= 80

Odds Ratio = A/B divided by C/D = AD/BC = 30x80/10x60=4

Base Population

• General population or population subgroup

• Primary care population

• Mental health service population

• Psychiatric Case Registers

Epidemiological Research Design

• Experimental studiesClinical trials

– Randomization– Placebo– Blinding

• Single, double, tripple

Types of Epidemiological Studies

• Observational studies– Cross-Sectional Studies– Longitudinal Studies

• Prospective• Retrospective

• Case-Control Studies– Establish risk factors, not rates of disorder

• Case Register Studies

Design of a Community Survey

• Defining the base population (sample frame)• Sampling method• Case Identification/definition (ascertainment)• Survey Instruments• Contact and Consent• Interview• Data entry and analysis

The Problem of Psychiatric Case Definition

• Informal clinical judgement (Essen Moller, Hagnell,1966)

• Categorical and dimensional approaches (Srole et al, 1962)

• Reliability and Validity

• Computerized Diagnosis

Sampling

• Individuals, households, addresses,postcodes

• Random sampling• Stratified sampling• Comparison with base population

characteristics• Sampling error, non cooperation, and

distorted data from respondents

Instruments

• Questionnaires– GHQ

– HAD

– Beck’s inventories

– Symptom checklists

• Rating scales– Hamilton’ Depression Scale

– Bech Raphaelson Mania Rating Scale

Establishing a causal link between event and disorder

Case

Yes No

Yes a b

Exposed

No c d

Instruments

• Interviews– Structured (same questions asked of all

subjects)– Semi-structured ( same topics covered with

some leeway for follow on questions– Unstructured ( interviewer use their own

clinical judgement)

Structured Interviews

• Can be applied by trained lay persons• Statements and wording pre-set• Standard• Examples:

– DIS– CIDI – SCID– SADS

Semi-Structured interviews

• PSE

• SCAN

• CIS

Issues of Reliability and Validity

Reliability

Inter rater agreement

Test-retest

Validity

Construct

Content

Correlation with gold standard

Sensitivity and Specificity

• Cases by screening test

Yes No

Cases by interview Yes a(TP) b(FP)

No c(FN) d(TN)

Sensitivity : a/a+b

Specificity : d/c+d

+ve predictive value a/a+c

-ve predictive value : a/b+d

Chicago Study : Faris and Dunham (1922-1934)

• 35,000 admissions to mental hospitals• 1st admissions for schizophrenia highest in

inner city areas within lowest socioeconomic groups

• Led to the social drift and social segregation hypotheses

• And to the social causation and social selection theories

Midtown Manhattan: Rennie and Srole (1954)

• 1660 adults, structured interview by non psychiatrists

• Incidence of mental disorder increased with age

• Low socioeconomic group had 6 times as many symptoms as those in the high groups

New Haven: Hollingshead and Redlich (1950)

• Social class and prevalence of treated mental disorder

• Census of psychiatric patients, community survey, survey of psychiatrists and controlled case study

• Described 5 distinct social classes and found neurosis in high classes, and psychosis more prevalent in lower classes

• 15.1% of population above 26 showed evidence of mental disorder

Stirling County: Alexander Leighton

• 20,000 rural persons ,non-clinicians, structured interview, later psychiatrist rating

• 24% had notable impairment, and 20% needed psychiatric attention

• Women>men, morbidity increases with age and poverty

NIMH-ECA Survey : Regier et al 1998-

• 20,000 from various sites across the US

• Structured interview, DIS, lay interviewers

• 15% one year prevalence of mental disorder in US population, 1/5 untreated, 1/5 treated by mental health, 3/5 primary care

• Depression :women 2/men1

• Men more alcohol and substance misuse

Psychiatric Morbidity in Upper Egypt (n=5291)

18.2%

0.4%

2.1%

8.8%

6.9%

17.4%

0 5 10 15 20

Subclinical

Likely case

Case

Case in remission

Case in treatment

Total caseness

Subclinical Likely case Case

Case in remission Case in treatment Total caseness

The Future of Psychiatric Epidemiology

• Molecular genetics and epidemiology

• Risk factors and dimensional measures of psychopathology

• Cross-national differences in the prevalence of disorder

• Changes over time (secular) changes in the pattern and prevalence of disorders

Group I :Design an epidemiological study to test the hypothesis: there is higher prevalence of psychosis in prisons compared to the general population.

The design should include detecting associations with potential risk factors for any excess of psychotic disorders in persons serving a prison sentence

Design an epidemiological study that could determine the prevalence and demographic correlates of psychiatric disorder in the general population.

Design a study to examine the following null hypothesis: The prevalence of psychiatric morbidity was the same in 1977 and 1985. How will you explain any changes in prevalence detected by the study