Independent variable | Log PR estimate† (SE) | p Value | ||

Log-binomial | Robust Poisson | Log-binomial | Robust Poisson | |

Log(rate) | 1.3132 (0.3362) | 1.5578 (0.4270) | <0.001 | <0.001 |

Log(volume) | 0.7715 (0.1960) | 1.4614 (0.3510) | <0.001 | 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, and calculating minus twice the difference in log likelihoods to get a χ

^{2}test statistic and p value. In case the log-binomial did not converge, 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, three were greater than unity for the robust Poisson method, and the largest was 1.82.