EPI202 Lab 3 Proposed Solutions.pdf - Epi 202 Lab 3 Practice Problems Proposed Solutions Note to students please read the following guidelines on when

# EPI202 Lab 3 Proposed Solutions.pdf - Epi 202 Lab 3...

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Epi 202 Lab 3: Practice Problems Proposed Solutions Note to students: please read the following guidelines on when it is appropriate to use the phrase ‘over the study period’. Going forward in the last class, we will deduct points both when the phrase is necessary but left out of your interpretations as well as when it is unnecessary and inappropriately included in your interpretations. “Over the Study Period” 1. Necessary for measures of association that are estimated using count-based data in order to describe the time period that they were calculated based on a. CIR/CID/OR in a closed cohort with no loss to follow-up b. OR in a cumulative-incidence sampled case-control study c. CIR as approximated from OR in a cumulative-incidence sampled case-control study where the rare disease assumption is met 2. Not necessary and often inappropriately used for rate-based measures (IRR/IRD) because time accounted for in calculation a. IRR/IRD in cohort study b. OR in an incidence-density or risk-set-sampled case-control study c. Rationale for not using “over the study period” with rates: The rate (and rate ratio or difference) does not apply to all individuals over the entirety of the study period, because not everyone contributed follow-up time throughout the entirety of the study period. Rate only applies to individuals over the person-time actually contributed. d. Ex: We are studying depression among sleep-deprived vs. non- deprived college freshmen in an open cohort active from 2000-2010. The study runs for 10 years, and each freshman contributes a maximum of one year to the cohort before they “age out”. e. IRR can be interpreted as the rate ratio of depression among exposed v. unexposed freshmen participating in this study.

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