Epidemiology 200A_worksheet6_blank

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Epidemiology 200A Worksheet 6 Case-control studies 1. The purpose of controls in a case-control study is to represent the distributions of _____________ and ____________ in the source population. (pick the single best answer) a. outcome; covariates b. confounders; person-time c. exposure; confounders d. exposure; person-time 2. The rare disease assumption is required for the estimation of the cohort risk ratio using the case-control odds ratio from a case-control study that uses the ___________ approach for sampling controls. (fill in the blank by picking the single best answer) a. risk-set sampling approach b. case-cohort sampling approach c. incidence density sampling approach d. cumulative control sampling approach 3. In which case-control sampling techniques can people counted as controls also be counted as cases? (select all that apply) a. case-cohort sampling b. cumulative sampling c. risk set sampling d. incidence density sampling 4. You are conducting a case-control study to estimate the effect of blueberry intake on colon cancer. Participants who exercise regularly were more likely to overestimate their blueberry intake on the dietary questionnaire (measurement tool used to assess blueberry intake for the study). Assume that regular exercise reduces risk of colon cancer. Select the type of bias that this overestimation likely introduced into the study. (select the single best answer) a. confounding bias b. selection bias c. information bias d. random error 5. You are conducting a case-control study to estimate the effect of blueberry intake on colon cancer. Participants who exercise regularly were more likely to eat blueberries regularly. Assume that regular exercise reduces risk of colon cancer. Select the type of bias that this likely introduced into the study. (select the single best answer) a. confounding bias b. selection bias c. information bias d. random error 1

Epidemiology 200A Worksheet 6 Case-control studies 6. Select all of the contrast measures you can directly calculate from a case- control study. (select all that apply) a. Risk ratio b. Risk difference c. Incidence rate ratio d. Odds ratio 7. True or false: Case-control studies are inherently inferior to observational cohort studies when your goal is to estimate causal effects of an exposure on a health outcome. False 8. Briefly describe a reason you might decide to conduct a case-control study compared with an observational cohort study to evaluate a given research question. When the outcome of disease is rare and you want to research the exposure of cases to the control group(who don’t have disease) in the same population. 2

Epidemiology 200A Worksheet 6 Case-control studies 9. You have an ongoing cohort study with 30,000 people. You have blood samples on all participants and you’d like to evaluate the association of a certain gene (exposure) with lung cancer (outcome). Genome sequencing is expensive, and you only have enough money to sequence the genomes of 2000 people. You decide to sample all of the participants with lung cancer (900) and 1100 of the participants who did not have lung cancer at the end of your study. Cases Controls E=1 600 700 E=0 300 400 a. Report the case-control odds ratio rounded to two decimal places: 600*400/300*700=1.14 b. What cohort measure does the case-control odds ratio reported in question 9a estimate, and why? (one short sentence) Cohort odds ratio because cumulative sampling. It measures the cohrort RR because rarity of disease less than 10%, its 3% c. Say that instead of sampling controls from people who did not have lung cancer at the end of your study, you decide you want to sampling controls in a way that respects person-time contributions of individuals involved. Briefly: (a) describe how you would do this, (b) what this method of sampling controls is called, and (c) what cohort measure the case-control odds ratio from this study would estimate and why. A. cases are identified as they occur and controls repsretns person time b. incidecnce density sampling c.cohort hazard ratio 3

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