Research however also challenges the notion that ethnic heterogeneity reduces public goods provision. Studies that find a negative relationship between ethnic diversity and public goods provision often fail to take into account that strong states were better at assimilating minorities, thus decreasing diversity in the long run. Ethnically diverse states today consequently tend to be weaker states. Because most of the evidence on fractionalization comes from sub-Saharan Africa and the United States, the generalizability of the findings is questionable. A 2018 study in the "American Political Science Review" cast doubts on findings that ethnoracial homogeneity led to greater public goods provision.