All descriptive statistics and associated standard errors, as well as regression models, were calculated using the SUDAAN statistical software package.29 Variance estimation utilized a Taylor linearization method appropriate for the multistage design of the surveys. Significance of between-survey differences in odds ratios (ORs) were assessed using two-sample z-tests applied to the beta coefficients (log OR). This is the large-sample equivalent of a two-sample t-test; z is the between-sample difference in effect size, divided by the pooled standard error.
