Back in the mid-1980s, Colonel Cooper mentioned in Guns & Ammo that NYPD's hit rate was 11%. He got a nastygram from them, in which they bragged about a 16% hit rate! The Colonel replied "Well, excuse us all to hell . . .out here, we talk about one hundred percent!"
Doing the math, you find that 84 out of every 100 rounds fired by NYPD cops goes somewhere they didn't want it to go. That's pretty close to a 9:1 ratio.
Hmmm . . .9 to 1 . . .one bad guy hit, 9 bystanders . . .
Now, to analyze this, remember that most cops are NOT into guns. They are issued a pistol and given some training. Most civilians who defend themselves in shootings ARE into guns, they bought their gun and the ammo after considering which to buy, and they likely spent a lot more time practicing. They also aren't distracted by all of the administrative Mickey Mouse that a cop faces after a shooting.