Estimate of Relative Risks (RR) & Odds Ratios (OR) for Exposed & Unexposed Patients.
Relative risk = [a/(a+b)]/[c/(c+d)].
Odds ratio = (a/c)/(b/d).
- Estimate of RR depends on having samples of exposed & unexposed patients, where the proportion of the patients with the outcome of interest can be determined.
- The RR is not applicable to case-control studies in which the number of cases & controls, & hence proportion of people with the outcome, is chosen by the investigator.
- For case-control studies a ratio of odds (OR) - the odds of a case patient being exposed divided by the odds of a control patient being exposed is used.
- Using a simple 2x2 table, RRs & ORs can be represented as shown above.
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