I just came across an interesting essay on Freakonomics called "The Cost of Fearing Strangers." In it, Stephen Dubner makes a point I've been making for years: We're more scared of strangers than people we know, but people we know are often more dangerous.
He provides a few useful statistics. In the US, a solid majority of murder victims knew their killers -- 3 victims knew their killers for every 1 killed by a stranger.
64 percent of women who are raped know their attackers, and 61 percent of women who are assaulted in other ways know their attackers. Men, on the other hand, are more likely to be attacked by strangers.
Yet for some reason -- probably a false belief that men can protect themselves effectively -- we as a society are much more worried about protecting women from strangers than we are about protecting men.
Most self defense programs focus too much on teaching women how to protect themselves from strangers, when learning how to read potentially dangerous behaviors in friends and acquaintances is more likely to keep you safe.