RISKY BUSINESS - MAKING SENSE OF ESTIMATES OF RISK

This article describes various indices of risk which is the probabilit y that a person will develop a specific outcome. The risk difference i s the absolute difference in risks between 2 groups and can be used ei ther to compare the outcome of 2 groups, one of which was exposed to s ome genetic or environmental factor, or to see how much of an effect a treatment may have. The reciprocal of the risk difference, the number needed to treat, expresses how many patients must receive the interve ntion in order for 1 person to derive some benefit. Attributable risk reflects the proportion of cases due to some putative cause and indica tes the number of cases that can be averted if the cause were removed. Finally, the relative risk and odds ratio reflect the relative differ ences between groups in achieving some outcome, either good (a cure) o r bad (development of a disorder).