PLINK [Purcell et al., 2007] was used to analyze the three datasets drawn from families (Add Health, NYS-FS, and SMOFAM). The QFAM total association test (–qfam-total) was used to conduct a family-based analysis that partitions the between family variance and the within family variance [Fulker et al., 1999] and is similar to that incorporated in the QTDT package [Abecasis et al., 2000]. This linear regression approach was ideal for this study because beta values from each family study analysis could be included.
