 There is also strong evidence that current GWAS are susceptible to population stratification. Because human populations exhibit ethnic or cultural subgroups with distinct allele frequencies, population stratification increases the likelihood that GWAS identify false positive SNPs. Not only is there evidence of population stratification among large groups of individuals of different biogeographic ancestries (Europeans, Asians, Africans), but populations are stratified within groups as well. For example, individuals of European descent would include both Parisians as well as English immigrants.