We then applied the item order that emerged from the cluster analysis on sample 1 to the genetic correlational results from sample 2, and observed the same two item clusters (lower triangle of Fig. 1), with very similar within and between item rg’s (overall mean rg = 0.62; range rg’s: 0.40–0.89; within clusters mean rg = 0.80, range: 0.73–0.89; outside of clusters mean rg = 0.58, range: 0.40–0.78). The genetically homogenous clusters thus replicated robustly within the UKB sample. All items had a relatively high rg with the sum-score (range: 0.73–0.89), but items assigned to clusters correlated even higher with their respective cluster, while rg’s with the opposite cluster were considerably lower (difference > .20), confirming genetic heterogeneity within the full item set (Supplementary Fig. 24; Supplementary Data 1). Genetic analysis of such genetically homogenous clusters may reveal genetic signals that are important for multiple items in one cluster but not for items in the second cluster, as we recently showed in ref. 19.
