A new NBER paper by Richard B. Freeman and Wei Huang looks at the ethnic diversity of research collaborators. They find that papers with more authors in more locations tend to be cited more:
This study examines the ethnic identify of the authors of over 1.5 million scientific papers written solely in the US from 1985 to 2008. In this period the proportion of US-based authors with English and European names fell while the proportion of US-based authors with names from China and other developing countries increased. The evidence shows that persons of similar ethnicity co- author together more frequently than can be explained by chance given their proportions in the population of authors. This homophily in research collaborations is associated with weaker scientific contributions. Researchers with weaker past publication records are more likely to write with members of ethnicity than other researchers. Papers with greater homophily tend to be published in lower impact journals and to receive fewer citations than others, even holding fixed the previous publishing performance of the authors. Going beyond ethnic homophily, we find that papers with more authors in more locations and with longer lists of references tend to be published in relatively high impact journals and to receive more citations than other papers. These findings and those on homophily suggest that diversity in inputs into papers leads to greater contributions to science, as measured by impact factors and citations.