For all the debate about what the U.S. Supreme Court says about the constitutionality of affirmative action, much of the action in the last two decades has been at the state level. Referendums have barred public colleges and universities from considering race in admissions decisions in states such as California, Michigan and Washington.

A new study in the journal Educational Evaluation and Policy Analysis finds that these bans have in fact been followed by the public colleges in what the research calls “post-affirmative action states.” In these states the relative advantage to being an underrepresented minority in odds of admission has seen a “substantial reduction” since various bans were enacted. This finding differs from the doubts of some observers – generally critics of affirmative action – who have suggested that colleges have found ways to continue to boost the admissions odds of minority applicants.

The study also found an impact on applicants from states near the post-affirmative action states – in cases where those states lack highly competitive colleges. And the study found no evidence that colleges scaled back their consideration of race in the immediate aftermath of the 2003 Supreme Court rulings in two cases involving the University of Michigan that upheld the constitutionality of considering race in admissions, but also set limits on its use.

The approach by Grant H. Blume and Mark C. Long, both of the University of Washington, is to compare the likelihood of minority and non-minority applicants being admitted to colleges in 1992 (prior to the state bans) and 2004 (after the Supreme Court’s 2003 rulings). They found that, in the 1992 cohort, underrepresented minority status (comparing students with similar test scores, grades and other characteristics) has a strong positive impact on the admission of applicants to colleges, once a certain level of competitiveness is reached. As the colleges become more competitive, the impact of underrepresented minority status goes up.

In the national sample for 2004, Blume and Long found small (and not statistically significant) declines in the impact of minority status. But in post-affirmative-action states, the impact was significant, such that minority applicants were not receiving very much of an advantage any more.

These findings suggest that states not facing outright bans did not adjust their use of affirmative action – even as some states did so, and the Supreme Court’s stance was not certain (at least until the 2003 rulings).

The scholars then looked at the impact on applicants from states that are adjacent to states that barred the consideration of race. They focused on this group because many college applicants, if not looking in state, go nearby.

Here the study found that in states such as Nevada and Arizona, affirmative action bans in states such as California had a notable impact. That’s because Nevada and Arizona don’t have colleges at the same competitiveness levels of admissions as does California, so those seeking that type of institution typically looked to California. There, they ran into the ban on consideration of race – so minority applicants experienced a notable decline in their ability to gain admission.

But in Oregon, also adjacent to California, minority students didn’t experience this loss. That’s because, the scholars write, private institutions such as Reed and Lewis and Clark Colleges are competitive in admissions and do consider race.