The measurement and interpretation of proportionate mortality.

The standardized proportionate mortality ratio (SPMR) is shown to be a summary measure which is a weighted average of age-specific proportionate mortality ratios which uses an internally derived set of standard weights. As with any summary measure, the SPMR is only meaningful when the stratum-specific values can be judged to represent a common value. When stratum-specific values are not homogeneous, the use of the stratum-specific values themselves is more appropriate than the use of a summary measure. A test for homogeneity of the age-specific proportionate mortality ratios is presented. The test also provides an estimate of the common value and its variance, when that single parameter can be presumed to exist. A procedure of external standardization is presented which uses weights derived from the standard population.