Measurement and expression of risk: optimizing decision strategies.

A significant proportion of the >6 million articles published annually present data in terms of risk and risk reduction. While the measurement of risk and risk reduction is often straightforward, there are a variety of ways that risk may be expressed. Risk is defined as the rate of an occurrence of a particular disease or adverse event and is determined by the number of events divided by the person-years or number of individuals in the at-risk population. The portrayal of risk can be achieved using different techniques but is typically provided in demographic maps, time-trend charts, or incidence bar graphs. Risk can be expressed in relative terms such as relative risk or absolute measures such as attributable risk or number needed to treat. Understanding risk determination as well as the differences in risk depiction and expression is necessary to ascertain the relevance of the data to one's clinical practice as well as to make optimal clinical and pharmacoeconomic treatment decisions. A review of terms, together with examples, is presented, such that clinicians evaluating the medical literature will be able to identify differences in the way that risk-related results are expressed and optimize the application of such evidence to their practice.