pubmed-article:11904847 | pubmed:abstractText | First-generation immigrants frequently have a lower mortality than the host population, in spite of a low socio-economic status. This is usually explained by (self-) selection into migration. If this were the case, the immigrants' mortality risk would increase with time under observation. A persistently low mortality could be due to a late entry bias: if migrants are enrolled in a study years after immigration, sick or socio-economically unsuccessful individuals may already have returned to their countries of origin. Mortality risk would then be inversely associated with length of stay in the host country before enrollment. | lld:pubmed |