age and FTND, in the US and Australian samples. The table shows that the mean FTND in cases is very similar across the two recruiting sites (US and Australia), although the proportion of cases and controls recruited differs. Also, the proportion of women differs in cases and controls. Therefore the variables site and sex are included as covariates in the genetic association analyses. Analyses using STRUCTURE (Pritchard et al., 2000) demonstrating no evidence of confounding population substructure are published elsewhere (Bierut et al., 2007). The study was carried out in compliance with the Code of Ethics of the World Medical Association and obtained informed consent from all participants and approval from the appropriate institutional review boards.
