August 23

HOW MANY times a year do U.S. police officers employ deadly force, and how many people die as a result? What are the races and ethnicities of those involved? How often are the objects of police force armed or unarmed? These are just some of the questions people have asked in the wake of the fatal shooting of Michael Brown in Ferguson, Mo. — and they are perfectly reasonable queries.

What’s less easy to understand is that no one can answer them precisely. This data-driven society, in which retailers know the buying habits of their customers down to the last dollar and police use sophisticated software to target crime “hot spots,” apparently lacks solid and systematic information about police shootings.

A 1994 statute instructed the Justice Department to gather data on the “excessive” use of force by police officers around the country and to publish it annually. Stunningly, the department has never done that, whether because of resistance by state and local governments, lack of funding or the admitted vagueness surrounding the term excessive.

As The Post’s Philip Bump discovered when he attempted to pin down the numbers, the closest thing to an authoritative national estimate for killings by officers is the figure for “justifiable homicides” by police that the Federal Bureau of Investigation publishes each year. That number has oscillated between 300 and 450 for most of the past quarter-century. But it’s an insufficient data point, because it’s based on voluntary reporting from only 750 of the nation’s 17,000-plus police agencies. And, of course, it seemingly doesn’t include any killings that were found to be unjustified.

In November 2011, the Bureau of Justice Statistics published figures on “arrest-related deaths” from 2003 through 2009, which did include information on the races and ethnicities of the deceased, as well as broad categorization of circumstances surrounding each case. The annual average of homicides attributable to police, 422, is consistent with the FBI reports. But there were holes in these data, too — not all states reported each year, for example — and the figures have not been updated in a half-decade. The Justice Department’s legal authority to require quarterly reports from the states expired in 2006.

This won’t do. Right now, the United States is embroiled in a necessary but, at times, emotional debate about the use of deadly force by police against civilians. Precise, complete and reliable official information must inform that discussion. Data are also, crucially, needed for the Justice Department’s exercise of its statutory authority over police suspected of a “pattern or practice” of excessive force. If Congress does nothing else in response to the tragedy in Ferguson, it must legislate, and fully fund, the collection of this information.