the PRS-CS polygenic score in Add Health and COGA, respectively. Thus, we conclude that there was some, but not extreme, attenuation when predicting the phenotypic externalizing factor within families. Also, the association of the quasi-replication polygenic score constructed with the 579 EXT SNPs remained significant and basically did not attenuate in within-family models (for this score, the standardized difference between βWF and β was −0.338 (two-sided P = 0.735) and 0.07 (two-sided P = 0.944) in Add Health and COGA, respectively).
