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11 epidemiology


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11 epidemiology

  2. 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. 3. Uses of Epidemiology1. Completing the clinical picture2. Community Diagnosis3. Secular changes in incidence4. Identification of Risk /Protective Factors/Prevention5. Delineation of syndromes6. Planning services
  4. 4. Epidemiology Terms• Rates and Ratios• Prevalence – Point – Period – Lifetime – Treated and untreated• Inception (Incidence)
  5. 5. Prevalence and Inception Rates• Persons » A ----------------------- » B --------------- » C ------------ » D ------ » E ____________________________ t0 t1 t2 t3
  6. 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. 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. 8. Base Population• General population or population subgroup• Primary care population• Mental health service population• Psychiatric Case Registers
  9. 9. Epidemiological Research Design• Experimental studiesClinical trials – Randomization – Placebo – Blinding • Single, double, tripple
  10. 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. 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. 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. 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. 14. Instruments• Questionnaires – GHQ – HAD – Beck’s inventories – Symptom checklists• Rating scales – Hamilton’ Depression Scale – Bech Raphaelson Mania Rating Scale
  15. 15. Establishing a causal link between event and disorder Case Yes No Yes a bExposed No c d
  16. 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. 17. Structured Interviews• Can be applied by trained lay persons• Statements and wording pre-set• Standard• Examples: – DIS – CIDI – SCID – SADS
  18. 18. Semi-Structured interviews• PSE• SCAN• CIS
  19. 19. Issues of Reliability and ValidityReliability Inter rater agreement Test-retestValidity Construct Content Correlation with gold standard
  20. 20. Sensitivity and Specificity• Cases by screening test Yes NoCases by interview Yes a(TP) b(FP) No c(FN) d(TN)Sensitivity : a/a+bSpecificity : d/c+d+ve predictive value a/a+c
  21. 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. 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. 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. 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. 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
  26. 26. 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
  27. 27. 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
  28. 28. Group I :Design an epidemiological study totest the hypothesis: there is higherprevalence of psychosis in prisons comparedto the general population.The design should include detectingassociations with potential risk factors forany excess of psychotic disorders in personsserving a prison sentence
  29. 29. Design an epidemiological studythat could determine the prevalenceand demographic correlates ofpsychiatric disorder in the generalpopulation.
  30. 30. Design a study to examine thefollowing null hypothesis: Theprevalence of psychiatric morbiditywas the same in 1977 and 1985.How will you explain any changesin prevalence detected by the study