1. PSYCHIATRIC
EPIDEMIOLOGY

2. 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

3. 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

4. Epidemiology Terms
• Rates and Ratios
• Prevalence
– Point
– Period
– Lifetime
– Treated and untreated
• Inception (Incidence)

5. Prevalence and Inception Rates
• Persons
» A -----------------------
» B ---------------
» C ------------
» D ------
» E
____________________________
t0 t1 t2 t3

6. 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)

7. Odds ratio
• Odds Ratio
A= 30 B = 60
C= 10 D= 80
Odds Ratio = A/B divided by C/D = AD/BC =
30x80/10x60=4

8. Base Population
• General population or population subgroup
• Primary care population
• Mental health service population
• Psychiatric Case Registers

9. Epidemiological Research Design
• Experimental studies
Clinical trials
– Randomization
– Placebo
– Blinding
• Single, double, tripple

10. 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

11. 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

12. 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

13. Sampling
• Individuals, households,
addresses,postcodes
• Random sampling
• Stratified sampling
• Comparison with base population
characteristics
• Sampling error, non cooperation, and
distorted data from respondents

14. Instruments
• Questionnaires
– GHQ
– HAD
– Beck’s inventories
– Symptom checklists
• Rating scales
– Hamilton’ Depression Scale
– Bech Raphaelson Mania Rating Scale

15. Establishing a causal link between event and
disorder
Case
Yes No
Yes a b
Exposed
No c d

16. 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)

17. Structured Interviews
• Can be applied by trained lay persons
• Statements and wording pre-set
• Standard
• Examples:
– DIS
– CIDI
– SCID
– SADS

18. Semi-Structured interviews
• PSE
• SCAN
• CIS

19. Issues of Reliability and Validity
Reliability
Inter rater agreement
Test-retest
Validity
Construct
Content
Correlation with gold standard

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

28. Psychiatric Morbidity in Upper Egypt (n=5291)
Total caseness 18.2%
Case in treatment 0.4%
Case in remission 2.1%
Case 8.8%
Likely case 6.9%
Subclinical 17.4%
0 5 10 15 20
Subclinical Likely case Case
Case in remission Case in treatment Total caseness

29. 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

30. 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

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

32. 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