Well, getting back to the initial topic. Again.
There is not a lot of information, especially regarding citizens' marksmanship. Here are a few interesting pieces of information:
1. Peace officers involved in violent encounters had a hit rate of 39-41% at an average range of 21-25 feet.
2. The assailants of peace officers involved in the same encounters had a hit rate of 68-91% at an average range of 14-15 feet. It was noted in the study that the average range was misleading, as one incident occurred at 70 feet (no hits). The majority of the incidents occurred at 0-10 feet. Police average distance was longer because the range increased as the encounter played out.
In the encounters studied, 90% of the time the assailant fired first. So, police officers had a hit rate of about 40% while under fire (sometimes wounded, sometimes fatally). The study notes that the assailants generally were 'point shooters' (didn't use sights), had been in previous gunfights, and practiced.
(note: above information from 'Violent Encounters' published by the FBI)
For citizens, data is sparse and wildly variable. Using BJS information, citizens use their guns for defensive purposes 62,300 times per year. In that time, they commit about 200 justifiable homicides. There are anywhere from 40 million to 80 million gun owners in the United States. In any year, approximately 19 million of them actually shoot the guns they own (i.e. go to a range or some place and pull the trigger...). I found no information on hit rates by citizens in violent encounters.
Continuing with justifiable homicides, citizens generally commit theirs while interrupting a crime. Peace officers generally commit theirs while stopping an assault.
I think one of the misapprehensions I see in this thread is the belief that citizens are better shooters than peace officers because of experience with both groups at the range. The average gun owning citizen doesn't go to the range, and doesn't shoot their gun.
The fact that someone is at the range indicates they are already well above average for citizen gun owners.
I see a lot of comments denigrating peace officers' marksmanship, so I suggest a course of fire based on a friend's personal experience. In his first gunfight, he had 0% hits in 15 shots from a high-cap .45. Of course, looking back, he understands why and he has made adjustments. He has done better since. Anyway, you will need a friend. He will need a 12 gauge pump shotgun loaded with 7 1/2 shot. Place one B-27 target at 20 yards. Keep your gun at low-ready. You'll need a nearby barricade for cover. When your friend is ready, he should shoot you twice with a 12 gauge shotgun in the leg and back. You should then move to cover, and fire at the B-27 silhouette. Your friend should shoot you any time you expose part of your body outside the cover. I haven't tried this myself, because I note my friend has arthritis in the knee, hip, and hand from where he was shot. He still occasionally has surgery on his knee when a shot pellet works its way behind his kneecap. (note: please don't really try this. Its meant for illustrative purposes only.)
And so, summing up all this information (plus information from this thread and others like it)...I conclude:
The average peace officer is a better marksman than the average citizen gun owner.
The 'committed shooter' citizen gun owner is a better marksman than the average peace officer. By 'committed shooter', I mean one that actively participates in shooting sports, attends shooting schools on some frequency, and/or gets to the range once per month (or maybe every other month...I'm flexible).
Once you get to the kind of level described by 'committed shooter', I conclude there isn't a difference in marksmanship skill between citizens and peace officers. (i.e. a 'committed shooter' peace officer will, on average, shoot the same as a 'committed shooter' citizen).
At the very top end, I believe the best sport-shooters are citizens, not peace officers. I don't necessarily believe that those very best sport-shooters are better than the very best peace officers in a gunfight. That's one for more speculation.
Regards
--Dan