There are three kinds of lies, according to Mark Twain, quoting Disraeli -- lies, damned lies, and statistics ...
Math has never been my forte, but sometimes even an arithmetical dullard can see something right in front of him. I got into a discussion with a fellow who allowed as how there are no more criminals now then when we were little tykes back in the fifties. It's the media -- notably the vile and liberal media -- that, lacking anything else to write about, trumpets every little thing. Our wives and daughters and property aren't at any more risk then they used to be, he said.
After I pointed out that most of the vile and liberal media are owned by conservatives, raising no small amount of consternation in his red state soul, I was able to allow that his theory didn't hold water.
Assuming that the percentage of hardcore criminals is about the same -- which research indicates is so -- then the logic fails. If, in 1950, there were 150,000,000 people in the U.S. plus or minus a few, and say, 1% of them were bad guys, then that works out to a million and a half cutpurses, footpads, and ne'er-do-wells. (The percentage isn't important here, only the ratio.)
If in 2009, the population was twice that and the percentage is the same, or even a bit less, vis a vis bad guys, then the total number is doubled, ipso facto.
Of course, there are other factors -- where you live matters. In Chicago there were 598 homicides in '08. In Beaverton, there were 2. Got more of a target pool in a bigger city, and income and education and like that matter. And rates go up and down. The 1970's were the worst for violent crime in the U.S. pretty much everywhere.
But still. There aren't fewer bad guys than there used to be. There are more.