# PUBHLTH 101 Lecture Notes - Lecture 12: Odds Ratio, Cohort Study, Relative Risk

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## Document Summary

Rr = 1 risk in exposed equal to risk in non exposed (no association) Rr > 1 risk in exposed greater than risk in non exposed (positive association; possible causal association) Rr < 1 risk in exposed less than risk in non exposed (negative association; possible protective association) Odds ratio or: in order to calculate a rr, we must have values for the incidence of the disease in the exposed and the incidence in the non-exposed. In case control study: we cannot calculate incidence in exposed & non-exposed: therefore, in case control study, we cannot calculate rr directly, we have to consider other type of measurement of association in a case-control study. In both ad bc represents the odds ratio (relative odds) in both cohort and case-control studies. Or = 1 the exposure is not related to the disease (no association) Or > 1 the exposure is positively related to the disease (positive association; possible casual association)