In most cases, tag SNPs chosen with the HapMap CEU panel were indeed “portable” to studies of common variants in other Europeans36,40. Similarity of a target population to a reference panel on which tag SNPs were selected, along with general LD levels in the population, were identified as important determinants of the portability to a target population of tag SNPs selected using a reference population41. LD in Europeans is moderate compared to other populations42,43, so that Europeans are not disadvantaged in the tag-SNP approach by this variable. Further, portability is enhanced in Europeans owing to the low level of population structure and the resulting high level of genetic similarity of most European populations to the CEU sample41.
