differences among point-prevalence estimates. The random-effects model assumes all prevalence estimates are influenced by unobservable factors that are specific to each survey. Additionally, we noted that some surveys changed the threshold for women in binge drinking questions, and that the BRFSS changed the gateway questions for alcohol use. These changes were dealt with using dummy variables in the regression equation, which necessarily assumes that the same wording change would have had the same effect in any given year. This is a face-valid but ultimately untestable assumption. Finally, we should note that all surveys based on self-reported alcohol use result in substantial under-reporting of consumption when compared with alcohol sales data (Kerr and Greenfield, 2007).
