There probably isn't much of any. And if the US is anything like Canada the rate will probably be double. In Canada, it's around 7% across the board. Most ex-military here, can latterly transfer to the RCMP as long as they pass the "snap" test. Which is to see if they're ready for reintegration into civilian life as a peace officer.
And while I can't give much insight into US policing, there are a few things I can add. Back about 10 years ago, you guys had a serious shortage of police officers. So bad, that many cities would hire ex-criminals, even those with felony convictions. Detroit was probably the most famous for this, but many other large cities did as well. There's was a rather large article on this in several of the policing mags(like blueline) in Canada on it.
With that, over the last 6 years the US has followed Canada on methods of hiring peace officers. Those are: Highly educated(college, or university grads), who have high or very high education levels but next to zero life experience. My personal favorite, was what a few of my friends told me. They were ex-hiring officers at two of the largest police services in Canada. They had one applicant who had a doctorate, had never lived on his own, was aged 32. And had never held a job. He marked them for "not qualified" the upper management which has become highly political overrode his objections and hired him on anyway.
The state of policing on both sides of the border is this: Fucked up, especially with the policy of hiring people with zero life experience.