[영문]Demographers and other analysts typically assume the stability of benchmark population estimates for making subsequent comparisons and estimates of change over time. However, fundamental changes in statistical classifications thwart this assumption and make such comparisons difficult, if not impossible. We review several important developments in the United States federal statistical system and discuss their effect on the data for racial and ethnic minority populations. We also present data from studies showing that these changes have potentially large impacts for certain smaller racial and ethnic minority populations. The conclusion notes several difficult challenges to data users posed by these findings.