we scored the SardiNIA data for the shorter questionnaires versions we found little differences in the results. Furthermore, given the universality of the five factors (17) and the commonality of genetic factors for each of a variety of other complex traits that have been studied in many populations, the major limitations are almost certainly the numbers of individuals studied in relation to the small effect sizes observed. Increasing power would likely require much larger initial and follow-up scans. As with other quantitative traits, meta-analysis of genome-wide association scans may provide an effective means to dissect these small effects (11, 41).
