Standardized Mortality Ratio

The standardized mortality ratio (SMR) compares the number of deaths actually observed in a study population with the number that would be expected if that population had experienced a standard set of age-specific death rates. It is the central output of indirect standardization: a single ratio, usually multiplied by 100, that says whether a group's mortality is higher or lower than a reference after accounting for its age structure. Because it needs only the study group's age distribution and total deaths — not stable age-specific rates within the group — the SMR is the method of choice when the group is small or its age-specific deaths are sparse.