11 epidemiology
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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