Social scientists have found a way to test, and confirm, one of the core claims of the Black Lives Matter movement. The rate at which unarmed black people are shot by police forces correlates with measures of structural racism by state. We might not know how to unravel that racism, but the findings at least point to some places to start.

In 2017 police in the United States killed 1,147 people of whom almost a quarter were black, twice the black proportion of the population. The ratio was even more skewed among unarmed victims. Whatever the arguments about the individual cases that have sparked protests, those statistics prove the problem.

However, debate has raged over whether the killings are motivated by police racism or reflect the increased time police spend in black neighborhoods as a result of higher crime rates. A team at Boston University tested the theories by creating a measure of structural racism and comparing this with the rate of killings.

The racism index is based on five measures: residential segregation, black and white incarceration rates, differences in educational achievement, economic inequality, and unemployment rates. A cumulative score for these, which surprisingly hasn't been calculated before, was compared with all fatal polices shootings of unarmed civilians between January 1, 2013, and June 30, 2017.

“For every 10-point increase in the state racism index, the Black-White disparity ratio of police shooting rates of people not known to be armed increased by 24 percent,” the authors report in the Journal of the National Medical Association. Nor was structural racism only having an influence through the way it brought officers in contact with victims. A correlation survived even after controlling for racial differences in arrest rates.

“The problem of police killings of unarmed Black victims should not be viewed merely as a problem of flawed action on the part of individual police officers, but more as a consequence of the broader problem of structural racism,” said senior author Professor Michael Siegel in a statement. “Unjustified homicide by police should be added to the long list of the public health consequences of societal racism.

"Our study suggests that this problem is not simply about the actions of individuals, but about the actions of all of society.”

As with any correlational study, this one opens up further questions about causation: Are there more black deaths at the hands of police in these states because growing up in more racially segregated communities increases prejudice, making police more likely to shoot anyone black? Or do the underlying historical factors that induce these structural injustices influence police training, which determines whether or not to use lethal force? Or is the mechanism something else again? Untangling such related questions is unlikely to be easy.

[H/T: Newsweek]