The covariates recorded included sex, age, and site (US or Australia). Forward selection using logistic regression indicated that sex and site were significant predictors of case/control status, as expected from Table I. Thus the covariate-corrected genetic analyses include these variables in the baseline model. With these main effects in the model, additional interaction terms such as age*sex were not significant. Figure 1 gives the distribution of FTND scores in male and female cases.
