Individuals within the study sample could fall into these categories because they chose not to identify their race, because the authors did not collect or report race and ethnicity data, or because the individual identified with a race other than one of the federal categories. Wherever possible, the Pathways Clearinghouse differentiates between cases where race and ethnicity were unknown or not reported, and cases where race and ethnicity were reported but fell into a different category. However, a number of earlier Pathways Clearinghouse reviews of studies published before 2000 did not differentiate between unknown, not reported, and other cases, instead reporting these as a single category.