Research conducted using the Migrant Acceptance Index, a metric developed by Gallup to assess the emotional impact of immigration on both migrants and native-born populations, found that newcomers to countries with the lowest migrant-acceptance scores rated their lives more positively than did native-born residents, but this positivity faded the longer migrants stayed. In countries with high acceptance scores, longtime migrants expressed more optimism about the future than either native-born residents or newly arrived migrants.