# March 4 - POPM*3240 March 4th Case-Control Studies Starting...

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POPM*3240 March 4 th Case-Control Studies - Starting with disease positive and comparing the exposure - Comparing the odds of exposure - Collect data and create a 2x2 table o Do a chi-square test - With case-control, we cannot calculate a relative risk o Because we are choosing how many disease and non-diseased individuals we see - Odds ratio – can use for all observational studies Data Analysis - Measures of effect can estimate attributable proportion (exposed) and can also estimate the population attributable fraction Biases Affecting Case-Control Studies - 3 main types: selection, information, confounding Selection Bias - Controls should be selected from the same study base/population as the cases - We want our control group to reflect the prevalence of the exposure in the non-diseased members of the population from which the cases are drawn sometimes this doesn’t happen Consider this: - Problem disease positive with increased pop consumption cell will go up, and will have a baised odds ratio Recall Bias - Problem recalling the past - Tend to remember the really good things or the really bad things Confounding - Must consider/try to prevent confounding bias - Can be controlled by one or more of: o Exclusion – only enroll male dogs instead of females if sex is a confounding variable o Matching – equalize the confounding variable between our 2 comparison groups o Analysis Stratification – do a separate odds ratio for exposure/outcome for large breeds of dogs and a separate for small breeds Regression analyses

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