Two economists have applied an income analysis to the graduates of historically black colleges -- and the scholars have come up with findings that could be problematic for the institutions or could suggest that they are remaining true to a historic mission.

The report found that the economic gains for a black student of attending a historically black college as opposed to a traditionally white institution changed dramatically between the 1970s and 1990s.

In the 1970s, when many of the most prestigious American colleges were just beginning to actively recruit black students, an economic-driven calculus would have sent a student to a black college. Now, according to the authors, the opposite is true, and graduates of black colleges have seen a significant decline in relative wages over the course of the two decades studied.

In addition, in a separate comparison, the scholars looked at elite black colleges and found significant declines in the proportion of students -- compared to black students at predominantly white institutions -- who would pick the same college again, who felt prepared for working alongside other racial groups, and who felt their leadership skills had been developed. (Black college students, however, in the latter comparison were more likely to be engaged in social or political activities.)

The question, of course, is: What does all of this mean?

The study was released Wednesday by the National Bureau of Economic Research and an abstract is available here.

The authors of the study -- Roland G. Fryer, an assistant professor of economics at Harvard University, and Michael Greenstone, a professor of economics at the Massachusetts Institute of Technology -- write that they conducted their analysis with the idea that decisions about historically black colleges should be made on more than on "theories and historical anecdotes." With the Supreme Court insisting in desegregation cases that black colleges provide a clear justification for their role, and public and private black colleges relying on federal funds (the latter primarily for student aid, not operating support), the authors write that the institutions need to be able to demonstrate their value. They used several longitudinal databases to come up with their conclusions.

On one level, the authors note ways in which their study does not reflect well on the black colleges. During the period covered by the study, the authors note, various measures of pre-college academic preparedness (such as test scores) went up at black colleges, so the relative income declines took place during a period when the opposite might have been expected.

One possibility for these trends, the authors write, has nothing to do with black colleges. The black students doing better financially and feeling better about their experiences elsewhere may primarily be a result of "improvements in traditionally white institutions' effectiveness at educating blacks," the authors write.

Leaders of historically black colleges agreed that the report may ultimately say as much about predominantly white institutions as about their own.

"Our schools educate students from disproportionately low-income backgrounds, many of whom have attended low-performing schools for their entire lives," Lezli Baskerville, president of the National Association for Equal Opportunity in Higher Education, said in a statement. "After more than 30 years of litigation, HBCUs have not received comparable funding to [traditionally white institutions]. The authors' analysis does not reflect the fact that HBCUs take students from where they are, bring them up to speed, and help them succeed with fewer resources. The authors also do not account for the economic and social costs of not helping underprepared students to get a college education, a role that HBCUs fill successfully more so than other institutions."

Baskerville said she hoped the two scholars would present their findings to black college presidents at a meeting later this year.

Michael L. Lomax, president of the United Negro College Fund, said he hasn't had time to study the report yet, and that it raises "complex" questions. He said that a key difference to consider is that in the first time period covered by the scholars, black colleges were attracting significant numbers of students from professional, middle class black families. These are now the students who "are cherry-picked by highly selective, prestigious institutions" that weren't looking for them in the 1970s, Lomax said.

Lomax stressed that there was nothing wrong with those institutions recruiting black students. "It's a wonderful thing for those students," he said.

But Lomax said that black colleges in the 1970s and today also make a lot of room for students who are the first in their families to attend college, who have academic talent despite having attended poor high schools, and who may have little or no money. Wealthier institutions can offer lots of aid -- and not all of it based on need -- to attract the better prepared and more affluent black students who once were a key part of a black college's student body, he said.

"Our institutions are for diamonds in the rough. The traditionally white institutions are looking for diamonds that have been pretty well cut already," he said.