Improving occupational standardized proportionate mortality ratio analysis by social class stratification.

The standardized proportionate mortality ratio (SPMR) method uses all deaths in all occupations and, therefore, all social classes to compute expected deaths in a single occupational group. By performing SPMR analysis within groups of occupations which are stratified by social class, the occupational contribution to the SPMR can be better identified. Mortality data from Washington state were used as illustrations.