that the difference in numbers of individuals of Irish ancestry was primarily responsible for the major difference in substructure observed in the NARAC cases and controls [23]. Controlling for this aspect of substructure the λgc in this individual set decreased from 1.15 to 1.07. Since the sample set had a disproportionately large contribution of participants of Irish ancestry we also examined a small set of individuals with nearly proportionate representation of Irish, German, Eastern European, and United Kingdom individuals. Similar to the results on the larger set of individuals, these PCA results showed a west-east gradient (Figure S4). Here however, there was no difference observed between the Irish and UK individuals. Thus, these results further indicate that the number of individuals from each individual group may partially alter relationships among individual groups.
