JUNIPER PUBLISHERS-BIOSTATISTICS AND BIOMETRICS OPEN ACCESS JOURNAL Be Wary of Using Poisson Regression to Estimate Risk and Relative Risk Authored By Leigh Blizzard Fitting a log binomial model to binary outcome data makes it possible to estimate risk and relative risk for follow-up data, and prevalence and prevalence ratios for cross-sectional data. However, the fitting algorithm may fail to converge when the maximum likelihood solution is on the boundary of the allowable parameter space.