Epidemiology 168 • Fall 1998 Midterm Answer Guide.html - University of North Carolina at Chapel Hill School of Public Health Department of

Epidemiology 168 • Fall 1998 Midterm Answer Guide.html -...

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University of North Carolina at Chapel Hill School of Public Health, Department of Epidemiology Epidemiology 168, Fall 1998 Midterm Exam Answer Guide 1. a. Manifestational criteria: disease definition and classification based on observable characteristics, such as symptoms, signs, history, labloratory findings, response to treatment, prognosis. Causal criteria: disease definition and classification based on the cause of the condition, b. Manifestational criteria: Examples are cancers, arthritis, cholescystitis, schizophrenia, depression, addiction, insomnia, . . . Causal criteria : microbial diseases for which the pathogen has been identified (syphilis, TB, malaria, yellow fever, influenza, etc.), lead poisoning, birth trauma, 2. (C)- Other choices are incorrect because controls in case-cohort studies are not matched to cases (A), contrrols are selected at random with both designs (B), and cases must be selected without regard to exposure (D). 3. New cases or events, population at risk or source population, passage of time 4. The size of the population may have grown (number increases even though rate does not); the age distribution of the population may have changed (e.g., influx of families with small children, outmigration of families with older children), so that age-standardized rate may not change but a greater proportion of the population may be in the higher risk age range (assuming that younger children have higher injury rates). 5. (D)- All of the above - use of prevalent cases requires that duration is not related to exposure, controls should provide estimate of exposure in study base, and rare disease assumption is required for OR to estimate RR (though not for OR to estimate IDR). 6. (B)- In a prospective cohort study, information on exposure is obtained before the outcome (breast cancer, in this case) has occurred. Therefore recall bias - different recall by cases and noncases - is not an issue. In a case-control study, cases and noncases may recall and report exposure with different degrees of accuracy. 7. a. A (retrospective) cohort study. b. CIR = (290/2,842) / (983/3,961) = 0.411 A cumulative measure ignores possible differences in length of follow-up between groups being compared. A crude measure ignores possible differences in the age distributions between men who have been exposed and men who have not. c. SMRs are an indirect method of standardization, since they are based on weighted averages for which the weights are taken from the population whose SMR is being computed rather than from a "standard" population. Unless the age (and in this case, age-calendar year interval) distributions for the populations whose SMR's are being computed are the same, then the weighted averages that make up the SMR's are based on different sets of weights and are not strictly comparable. Since age-interval distributions of exposed and unexposed workers may differ, their SMR's are not strictly comparable.
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