Reply #19: This article is a little old but i doubt the statistics have changed much

[johnd83]

It is a peer-reviewed article and cited by a large number of papers.

A total of 743 firearm-related deaths occurred during this six-year period, 398 of which (54 percent) occurred in the residence where the firearm was kept. Only 2 of these 398 deaths (0.5 percent) involved an intruder shot during attempted entry. Seven persons (1.8 percent) were killed in self-defense. For every case of self-protection homicide involving a firearm kept in the home, there were 1.3 accidental deaths, 4.6 criminal homicides, and 37 suicides involving firearms. Handguns were used in 70.5 percent of these deaths.

http://www.nejm.org/doi/pdf/10.1056/NEJM198606123142406

The fact that the particular armed guy was able to recognize the situation quickly enough was lucky. Even trained police mess up in the same situation. An average person does not have the years of training and experience.