AS A teenager, Roland Fryer had “unpleasant” run-ins with police. Officers pointed guns at him six or seven times. Even now, the youngest African-American to get tenure at Harvard wonders why police shout loudly at him as soon as he forgets to indicate when driving. But when the economist began researching racial differences in the use of force by police officers, he did not want his own experience to prejudice his findings. To understand how cops work he joined them on the beat in New Jersey and Texas.

Then he collected a lot of data. In a paper published on July 11th, Mr Fryer crunched police-generated data on almost 5m cases from 2003 to 2013 as part of New York city’s Stop, Question and Frisk programme. He then analysed how non-lethal uses of force—such as pushing, kicking and baton-wielding—varied by race. Based on the raw data, blacks and Hispanics were more than 50% more likely to encounter police force than whites.

This in itself was not proof of racial discrimination, notes Mr Fryer. The gap might be a result of what happened during the encounters; blacks might have been more likely to resist. And yet, after any such differences were accounted for, the results still suggested bias. Blacks were 17.3% more likely to incur use of force after controlling for the characteristics of the civilian (such as age) and the encounter (such as if they ran away, complained or hit an officer). Analysis of a national survey of citizens’ contact with police found even greater disparities in police use of non-lethal force. Mr Fryer adds that blacks who were reported by cops as being perfectly compliant with police instructions during their interactions were still 21.1% more likely than whites to have some force used against them. This points to racial prejudice.

What shocked Mr Fryer was when he looked in detail at reports of police shootings. He got two separate research teams to read, code and analyse over 1,300 shootings between 2000 and 2015 in ten police departments, including Houston and Los Angeles. To his surprise, he found that blacks were no more likely to be shot before attacking an officer than non-blacks. This was apparent both in the raw data, and once the characteristics of the suspect and the context of the encounter were accounted for.

Mr Fryer dug deeper into the data. He combed through 6,000 incident reports from Houston, including all the shootings, incidents involving Tasers and a sample in which lethal force could have justifiably been used but was not. What he found was even more startling: black suspects appear less likely to be shot than non-black ones, fatally or otherwise.

These findings need caveats. Houston is one city; there are no equally detailed data for the rest of the country (though findings in the other districts seem to support the conclusions). The city voluntarily submitted its reports; it may have been confident of its lack of bias. Critics of Mr Fryer’s work have pointed out that his paper does not address any bias in an officer’s decision to stop a black person in the first place—a common criticism of stop and frisk. Mr Fryer acknowledges that blacks are more likely to be stopped, but adds that his findings are consistent with other types of encounter between police and civilians.

In explaining why racial bias is present in all cases except shootings Mr Fryer suggests that it may reflect how officers are rarely punished for relatively minor acts of discrimination. When he shadowed cops on patrol, Mr Fryer was told repeatedly that “firing a weapon is a life-changing event”—and not only for the victim. Although activists argue that too many officers get off lightly when they harm civilians, cops find it hard to escape any scrutiny after discharging their weapon. More transparency and accountability are therefore needed, even when police encounter members of the public.

For racial discrimination by police is socially corrosive. Mr Fryer suggests that if blacks take their experience with police as evidence of wider bias, it can lead to a belief that the whole world is also against them. They may invest less in education if they think employers are biased too. It is more than 50 years since Martin Luther King spoke of blacks being “staggered by the winds of police brutality”. Those winds are still blowing.