Independent Variable

Log Prevalence Ratio Estimate^{†} (SE)

PValue



LogBinomial

Robust Poisson

LogBinomial

Robust Poisson


Log(Rate)

1.3132 (0.3362)

1.5578 (0.4270)

0.0006

0.0003

Log(Volume)

0.7715 (0.1960)

1.4614 (0.3510)

0.0002

0.0000

 * Wald tests were used for the Robust Poisson method, and likelihood ratio tests were used for the logbinomial method. The latter were obtained by fitting a model without the effect being tested. The logbinomial method failed to converge when both independent variables were in the model and when only log(Volume) was in the model. In these cases, the COPY method approximation was used.

^{†} The intercept estimate was 1.5147 for the logbinomial method and 1.8311 for the Robust Poisson method. Of the 39 probability estimates, 3 were greater than unity for the Robust Poisson method, and the largest was 1.82.