In addition to structural differences, the survey content used very different nomenclature, and therefore we believe our estimated error rates to be overestimates of the true error rate, because it is likely that some individuals choose to identify with one label but not the other (i.e., “African American” but not “black”). Discrepancies in the question nomenclatures are likely to increase the error rate. Furthermore, because the two surveys could be completed at different times, either before or after obtaining personal ancestry results, it is possible that viewing genetic ancestry results might have led to a change in self-reported ancestry. Such a change would be tallied as an error in our estimates, but instead reflects a true change in perceived self-identity over time. Overall, we expect that our survey data represent highly reliable ancestry information, with errors affecting fewer than 1% of survey responses.