of differing racial backgrounds was not even discussed in this meta-analytic compilation of the literature. The meta-analysis is representative of the broader historical problem of a lack of racial diversity in twin registries, especially in the United States and Europe. For example, the Virginia Twin Registry (now part of the Mid-Atlantic Twin Registry or MATR) and the National Academy of Sciences-National Research Council (NAS-NRC) Twin Registry originally limited participation to “Caucasian” and “White” twins, respectively.
