WITH budgets under strain, governments across the developed world want to reduce their jail populations. For the first time in decades, America and Europe are now releasing more prisoners than they are locking up. One way to ensure those ex-cons do not wind up back behind bars is to help them find work. But a body of new research suggests one increasingly popular way to promote this has worrying unintended consequences.

Forcing job applicants to declare they have a criminal record—whether or not it is relevant to the post—allows employers to filter out ex-convicts, it is argued, and prevents them finding the sort of work that would help them stay out of prison. So activists across the world have called for “ban-the-box” laws, which prohibit employers from inquiring about criminal histories prior to job interviews or offers.

Some 24 states and many municipalities in America have now introduced laws along those lines. They are also gaining favour in Europe. The British government has banned the question for civil-service jobs; the policy was the core of the previous prime minister’s plans to boost racial equality. As black people are more likely than whites to end up with criminal records—five times more likely in America—banning the box should help reduce bias, advocates say. But research suggests otherwise. Instead, such policies encourage racial stereotyping by employers that hinders minority groups from finding work.

A paper by Jennifer Doleac of the University of Virginia and Benjamin Hansen of the University of Oregon, published on August 1st, looked at the impact of introducing ban-the-box policies on labour-market data from America’s population census. It found that withholding criminal-record data from employers encouraged them to treat certain minority groups as if they were more likely to have criminal pasts. In areas where ban-the-box laws have taken effect, the study found, the probability of being employed has fallen by 5.1% for young, low-skilled African-American men, and by 2.9% for young, low-skilled Hispanic men. Such effects are stronger in areas with lower levels of racism historically, such as those with smaller black populations in the Northeast, Midwest and West.

Other research backs up this conclusion. Amanda Agan of Princeton University and Sonja Starr of the University of Michigan sent 15,000 fictitious job applications to employers in New York and New Jersey. Before ban-the-box was introduced in these states, white applicants received around 7% more callbacks than similar black applicants. But when the policy took effect the gap increased to 45%.

Research by other economists suggests the more information the better when it comes to giving minorities a leg up. A recent paper by Abigail Wozniak of the University of Notre Dame found that employers who were allowed to use drug testing in recruitment were up to 30% more likely to employ black people, and, when they did, pay them more. Another study, by economists at MIT, published in March, found that banning employers from checking the credit records of potential employees reduced black employment by up to a sixth. In short, banning the box alone is a “cheap fix that doesn’t work” as far as promoting racial equality is concerned, Ms Doleac concludes.