Standardized incidence ratio (SIR), also referred to as observed-to-expected (O/E) ratio (or relative risk)

• - Population incidence rates are used to estimate expected numbers of events, taking into account age, gender, and calendar year

• - Observed number of events (e.g., second primary cancers) compared with number expected

• - If no increased risk exists (i.e., observed = expected), then SIR or O/E = 1

Absolute excess risk (AER)

• -

  \(AER\ =\ \frac{(observed\ {\mbox{--}}\ expected\ second\ cancers)}{No.\ of\ person-years\ at\ risk}\ {\times}\ 10,000\ =\ Excess\ no.\ of\ second\ cancers\ per\ 10,000\ patients\ per\ year\)

• - If no increased risk (i.e., observed = expected), then AER = 0

Percentage of patients diagnosed with event of interest in specified time interval Example: 25-y cumulative incidence of solid tumors among 32,591 patients with Hodgkin lymphoma was 11.7%.*