The VAFTND subjects were selected from the same sources as the VAANX-ND sample. This sample included almost all regular smokers who had FTQ/FTND assessments but were not used in the VAANX-ND sample. We excluded those subjects who themselves or their cotwins were used in previous sample panels to maintain the independence of these samples so they can be used to verify results obtained from previous panels. As in the previous panels, for each twin pair, only one twin was selected. The distributions of the IANGF and FTND scores in the two samples are compared in Supplementary Figure S1. The subjects in both samples were adults, with ages between 18 and 65 at the time of FTND ascertainment and all of them self-reported European ancestry.
