SMHS OR RR
Scientific Methods for Health Sciences - Odds Ratio and Relative Risk
HS 550: Fundamentals
Odds Ratio/Relative Risk
1) Overview: The relative risk is measure of dependence which allows us to compare probabilities in terms of their ratio (P_1/P_2 ) rather than their difference (p1 – p2). The relative risk measure is widely used in many studies of public health. Another way to compare two probabilities is in terms of the odds. If an event takes place with probability p, then the odds in favor of the event are p/(1 - p). The odds ratio is the ratio of odds for two probabilities.
Motivation: Suppose we study Brain Cancer in the context of cell phone use. The table below illustrates some (simulated) data. One clear healthcare question in this case-study could be: “Is cell phone use associated with higher incidence of brain cancer?” To address this question, we can look at the relative risk of cell-phone usage.
| Brain cancer (BC) | Total | |||
| Yes (A) | No | |||
| Cell Phone (CP) Yes | 18 | 80 | 98(B) | |
| Cell Phone (CP) No | 7 | 95 | 102(C) | |
| Total | 25 | 175 | 200 | |
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