IT IS well known among labour-market wonks that black Americans are less likely to be employed than members of other racial groups. The unemployment rate for blacks sits at 7.1%, compared with 3.8% for whites. What is not known, however, is why. One straightforward cause would be lower levels of education: only 23% of African-American adults have at least a bachelor’s degree, compared with 36% of whites. However, a recent paper by Tomaz Cajner, Tyler Radler, David Ratner and Ivan Vidangos, a group of economists at the Federal Reserve, finds that differences between races in schooling alone are not nearly large enough to account for the size of the disparity.

Using American census data from 1976 to 2016, the authors built a statistical model using four factors they expected to account for variations in unemployment between racial minorities and whites: education, age, marital status and the state a person lives in. Among men, these variables collectively explained around three-quarters of the difference in joblessness rates between Hispanics and whites—but only about one-fifth of the gap between blacks and whites.

The authors put forward three possible reasons for this stubborn discrepancy. First, they suggest that nominal educational attainment could be a poor measure of labour-market skills: schools vary widely in quality, and those in majority-black districts tend to underperform on standardised tests. A second potential reason is mass incarceration. Around one in three black men spend time behind bars during their lives, which severely hampers their employment prospects upon release.

The third possible explanation is outright discrimination. One study in 2004 provided strong evidence that racism among employers is at least partly to blame. The authors responded to “help wanted” advertisements in newspapers in Boston and Chicago with fake resumes. They gave names common to black Americans to some fictitious applicants, and names common to whites to the rest. Every other detail was identical. Sure enough, the candidates with stereotypically white names received 50% more job interviews.