Ignorance about the extent of racism in history might explain why some people perceive less racism today than others, researchers say.

To examine possible reasons why different groups see the reality of racism differently, the researchers recruited college students — 199 of European descent and 74 of African descent — to complete a true or false black history test. Some statements in the test covered well-documented, factual incidents, while other items discussed made-up but plausible events. The student participants also completed assessments their self-esteem regarding their racial identity as well as surveys to measure their view of systemic racism and isolated incidents of racism.

Historical knowledge predicted racism perception for both African Americans and European Americans, the researchers found, and overall, the African-American students were better at identifying historically true events. African-American students who reported greater relevance of racial identity also perceived more racism, while European-American students who placed greater importance on their racial identity saw less racism, especially on a systemic level, the researchers said.

The results suggest that knowledge of historically documented racism partially may help explain the relationship between someone's race and their perceptions of racism.

"Survey research consistently documents that, relative to white Americans, people from historically oppressed racial and ethnic minority groups tend to report less satisfaction with race relations, see social inequality as a greater problem, and see more racism in incidents, such as legislation targeting undocumented immigrants and 'stand your ground' laws," wrote the University of Kansas-led research team.

"Although popular and scientific understandings tend to portray ignorance as a lack of knowledge, this work emphasizes that ignorance itself is a form of knowledge that makes it possible to ignore or remain unaware of things that might otherwise be obvious," the researchers added.

The study was detailed online last month in the journal Psychological Science.

Follow LiveScience on Twitter @livescience. We're also on Facebook & Google+.