Interesting. This is what I've often though to be the case, but backed by a lot of actual, solid numbers. The magnitude of the effect is quite amazing. I guess even the possibility of someone being able to defend him/herself makes potential criminals reconsider. I suppose it has to do with risk to reward ratio. In Poland, if you decide to rob someone, the worst thing that would normally happen would be that you get beaten up and put in jail (not even for particularly long). If you try that in the US, especially in a gun-rich area, that might be the end of you right there. This is why I'm for gun registration and mandatory training, not gun removal. It is more about accident prevention than anything else since guns, unfortunately, also tend to introduce another way for idiots to hurt themselves and others by accident.