guns vs. crime
I agree with 7shooter, the definitive book on guns vs. crime is by John Lott. The details are spelled out on the specific issue you raised.
Carry decision
I have the S&W642, the Shield in .40 and Glock 19 & 22. The 642 is more compact than the Shield and best for me for summer carry in a pocket holster. The Shield's long grip makes it somewhat large for pocket carry in jeans or shorts. I plan to switch to the Shield when cooler...