A bar chart showing the breakdown, in terms of race and ethnicity of participants, for the 252 studies that provide this information. More than 60 percent of study participants are white. Out of more than 250 studies, published from 1990 to 2017, just one participant identified as Native American.
Data are based on 252 studies, published from 1990 through 2017, that reported the race or ethnicity of participants.