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unit 8 additional answers - U nit 8 Fall 2010 Quest ions...

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Click to edit Master subtitle style Unit 8 Fall 2010 Questions and Answers
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n Confounding Definition and identification of confounding Determining if a variable is a potential confounder Ways to control for confounding and when: randomization, restriction, matching (design), stratification, multivariate analysis, direct and indirect standardization Mantel-Haenszel OR/RR OR for matched studies and McNemar’s test Definition and mechanics of rate adjustment: direct and indirect n Effect modification Definition and identification of effect modification Understanding the difference between effect modification and confounding Evaluation of effect-modification through stratified analysis Understanding when to report effect-modification and when Study Guide
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Confounding is: n Mixing of effects of extraneous factors with the effect of interest. n Change in an effect measure upon stratification or adjustment for extraneous factors n Variables that can cause or prevent the outcome of interest, are not intermediate variables, and are associated with the exposure(s) under investigation
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Confounding is: n Mixing of effects of extraneous factors with the effect of interest. n Change in an effect measure upon stratification or adjustment for extraneous factors n Variables that can cause or prevent the outcome of interest, are not intermediate variables, and are not associated with the factor(s) under investigation n A nuisance effect that must be eliminated in order to obtain a more valid estimate of the effect measure n All of the above
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How do we identify whether confounding exists? n Know the literature well. Understand what other risk factors are related to your  outcome Understand how other risk factors are related to your  exposure Figure out biologically plausible DAG. n Know your data well. Perform univariate, bivariate analyses to characterize  distributions of variables in each comparison group  (or cohorts); ways that single variables are related to 
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Which DAG shows confounding? E PCF D E D PCF PCF E D YES/ NO YES/ NO YES/ NO
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Which DAG shows confounding? E PCF D E D PCF PCF E D YES/ NO YES/ NO YES / NO Salt intake Hypertensio n Stroke PCF intermediate Hypertensio n Stroke Disability PCF occurs after E and D Smoking OC use Stroke Smoking related to OC and stroke
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n Smoking is associated with oral contraceptive use (say smokers are more likely to use OCs) – IN THE DATA SET n Smoking is an independent risk factor for stroke (among non-OC users) n Smoking is not the result of OC use (PCF is not the result of E) (not an intermediate variable)
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Is obesity associated with cardiovascular mortality? n Note: Hypertension may be a PCF.
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