PC analysis was applied in the genome-wide scan sample of N = 4,763 to characterize the genetic distances between persons within the sample. The first 20 PCs were analysed in association with birth length, adult height, PHV1, PHV2 and age at PHV2 by sex. In addition to first five PCs, the PCs that were associated with one or more of the growth outcomes in either sex (PCs 11, 13 and 15) were adjusted in all SNP association analyses to control for population structure (see the recommendation by Novembre and Stephens [31]). Additional adjustment for socio-economic status at birth (SES) did not change the results essentially and was not applied. Unpublished data on this cohort show that adjustment for PCs partly corrects for SES in the (genome-wide) analysis of adult height due to a correlation between SES and some of the PCs. Adjustment for PCs also corrects for parental geographic location.
