Normalized residuals (i.e. mean 0, variance 1) were used for all variables to facilitate analyses in MERLIN-REGRESS (Sham et al., 2002). Univariate outliers with z-score values exceeding ±3.3 (less than 0.1% of the dataset) and bivariate outliers (less than 0.4% of dataset) were excluded from the linkage analyses. Bivariate, or within-family, outliers are defined as sibling pairs, or QISPs, for whom the squared phenotypic difference is much larger than expected from the population correlation. The method used for identifying these outliers is described in detail in Benyamin et al. (2008). For outlying QISPs, data for the individual with the largest deviation from the mean was removed.
