Standardized mortality ratio

The standardized mortality ratio is the ratio of observed deaths in the study group to expected deaths in the general population.

This ratio can be expressed as a percentage simply by multiplying by 100.

The SMR may be quoted as either a ratio or a percentage. If the SMR is quoted as a ratio and is equal to 1.0, then this means the number of observed deaths equals that of expected cases. If higher than 1.0, then there is a higher number of deaths than is expected. SMR constitutes an indirect form of standardization. It has an advantage over the direct method of standardization since age-adjustment is permitted in situations where age stratification may not be available for the cohort being studied or where strata-specific data are subject to excessive random variability.