The disparity is unlikely to be intentional on the part of IRS staff, says study author Daniel E. Ho, professor of law at Stanford Law School and faculty director of the Stanford RegLab.

“The IRS should drill down to understand and modify its existing audit selection methods to mitigate the disparity we’ve documented,” Ho says. “And we’ve shown they can do that without necessarily sacrificing tax revenue.”

Although there have been long-standing questions about whether the IRS uses its audit powers equitably, Ho says, the private nature of tax returns and the confidentiality of the IRS’s approach to audit decisions made it difficult to study.

“Racial disparities in income are well known, and what the IRS chooses to focus on has big implications for whether audits complement, or undercut, a progressive tax system,” Ho says.