The PS population distributions of the four traits considered here, calculated on the whole genomes of our reference panel and standardized on the European populations (CEU, IBS, TSI, light blue boxes in Fig. 2) show that the effect sizes ascertained on European populations may generate spuriously positively- or negatively-shifted PS distributions in non-European groups (i.e. YRI, LWK, CHB...), as observed before12. As mentioned in the introduction, this phenomenon is combined with poor predictive performance of PS based on European effect sizes applied to those non-European populations18. The same pattern is observed in Egyptians, Ethiopians, and African-Americans, most remarkably for T2D (Fig. 2a), where the PS distribution can be described as a linear combination between a 0-centered European and a positively-shifted African distributions. When computing aspPS instead, the two ancestries always returned distributions shifted in opposite directions, each towards the population-wide values of non-admixed European and African populations. This cannot be attributed to a casual fragmentation of the genome: shifts towards or away from 0 are found significant in most cases when comparing with simulated aspPSs distributions obtained assigning a random
