A comparison of two methods for estimating prevalence ratios

Table 3 Comparison of log-binomial and Robust Poisson methods for analysis of vaso-constriction associated with inspired air*

Independent Variable	Log Prevalence Ratio Estimate^† (SE)		P-Value
	Log-Binomial	Robust Poisson	Log-Binomial	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 log-binomial method. The latter were obtained by fitting a model without the effect being tested. The log-binomial 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 log-binomial 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.