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Next: Facility Comparison Analyses. Up: Statistical Methods Previous: Traditional SMR Analyses.

Grouped Data Poisson Regression.

The second and third approaches use Poisson regression methods [9,10,11,12] to describe the joint effect of several risk factors on cause- specific mortality. The general form of the regression function is

 

where represents the unknown mortality rate, is the number of deaths, and denotes the person-years at risk in the cell of an ADS. The i subscript refers to age, the j subscript indicates the dimensions of the ADS that correspond to factors of secondary interest (e.g., birth-cohort, SES) and the k subscript indicates exposure related covariates that are of primary interest, i.e. facility, internal exposure, and external exposure. The ''external/internal" model is used---[12], chapter 4---in which the baseline rates are proportional to known external standard rates , and the are treated as observed values of Poisson variates with expectation given by Eq. 1. For a given cell in the ADS, the value of will also depend on birth cohort. This approach has two advantages. First, it is not necessary to provide a parametric description of the age component of the baseline rates, and second the ''intercept" terms (when all explanatory variables are at their reference level) provide estimates of the SMRs for the internal control group.