Despite widespread media coverage of police shootings, no one knows for sure how many Americans are killed by police officers each year. That’s why FBI director James Comey’s announcement this week that the FBI plans to collect more data related to police shootings was initially encouraging to policy analysts like me. Unfortunately, it doesn’t look like Comey’s proposal will provide accurate numbers.

The FBI’s Uniform Crime Reporting (UCR) program does include data on the number of police officers killed on the job and the number of “justifiable homicides” committed by officers, but this information is not very helpful because the FBI relies on law enforcement agencies to voluntarily hand over the information. Perhaps unsurprisingly, not every police department complies.

Those departments that do report data, however are asked to report police shootings which take place in their jurisdiction. As the Wall Street Journal  pointed out in December last year, some California Highway Patrol shootings may not be accurately reported because the shootings take place in a location under another department’s jurisdiction. The report showed that the inefficiencies in the reporting for the UCR program results in hundreds of police killings being left uncounted.

Regrettably, Comey seems to be doing little to provide law enforcement agencies with incentives to volunteer more accurate use-of-force data. Given the United States’ federalist system, the FBI cannot currently demand that law enforcement agencies hand over data on use-of-force incidents.

While government data on police killings is poor, two newspapers are keeping track of such incidents this year. The Washington Post is collecting information on police shootings (741 so far this year) and The Guardian is tracking all police killings (875 so far this year). For the time being, it looks as if the best source for police killings in the United States will be non-government projects like these.

Comey’s call for better data on police killings should be welcomed. It’s frustrating that amid important discussions on much-needed reforms to police accountability, tactics, and training that information about police killings remains so unreliable.

However, Comey has little influence on what data state and local law enforcement agencies choose to release. As much as he should be applauded for his concern about the state of reporting on police shootings, it’s unlikely that his rhetoric alone will produce the desired results.