We often use the odds ratio and relative risk when performing an analysis on a 2by2 table, which takes on the following format The odds ratio tells us the ratio of the odds of an event occurring in a treatment group to the odds of an event occurring in a control groupIt is calculated as Odds ratio = (A*D) / (B*C) The relative risk tells us the ratio of the probability ofTherefore, odds ratios from most casecontrol studies can be interpreted as risk ratios However, if a study outcome is common, the odds ratio will be further from 1 than the risk ratioOdds Ratio Odds Ratio for comparing two proportions OR > 1 increased risk of group 1 compared to 2 OR = 1 no difference in risk of group 1 compared to 2 OR < 1 lower risk ("protective") in risk of group 1 compared to 2 In our example, p 1 = proportion of women receiving SAT p 2 = proportion of men receiving SAT OR pp pp pp pp = − − = − − 11 22 12 21 1
The Difference Between Relative Risk And Odds Ratios The Analysis Factor
