Table 3.

Common measures of risk

• SIR: the ratio of the observed number of cases of the outcome of interest to the expected number in an age-, calendar period- and sex-matched general population under observation for a specified interval.
• SMR: the ratio of the observed number of deaths from the outcome of interest to the expected number of deaths based on age-, calendar period-, and sex-specific mortality rates for the country.
• AER: the absolute number of excess cases (i.e., the observed number–expected number divided by person-years at risk times 10,000) or deaths for a given quantity of person-years of follow-up.
• Cumulative incidence: the percent or proportion of the population of interest with a specific outcome by a set point in time (i.e., 20% cumulative incidence of breast cancer by 50 years of age). When calculating the cumulative incidence of a given outcome, it is necessary to consider the risk of competing causes of death (i.e., death occurring before the outcome of interest). Statistical methods designed to evaluate overall survival that censor patients who die as equivalent to those lost to follow-up (e.g., the Kaplan–Meier method) will overestimate the cumulative incidence of nonfatal health outcomes, particularly if the study patients have a high risk of death from competing causes, or have prolonged follow-up.