Tuesday, April 24, 2007


If the United States had a Virginia-Tech-sized massacre every single year, how much would that increase the homicide rate? And how much would preventing a similar massacre every year reduce it?

The homicide rate is usually measured in persons per 100,000 population. The U.S. annual homicide rate has hovered around 6 per 100,000 for the last several years. There are approximately 300 million people in the U.S. That means an additional 32 homicides per year (the VT death toll) would increase the homicide rate by about 0.01 per 100,000. Likewise, if we succeeded in eliminating one VT-sized massacre per year, we would reduce the homicide rate by about 0.01 per 100,000. Hardly a blip, and well within the year-to-year variation in the homicide rate.

The effect would be exactly the same if 32 states each had one more (or one fewer) homicides per year. If that happened, nobody would even notice.

We could look only at the state of Virginia, of course. Another VT-sized massacre each year would raise Virginia’s homicide rate by about 0.4 per 100,000. Now that’s more significant, though still within the state’s year-to-year variation. If we looked only at the population of VT, the homicide rate would be obscenely higher. But these numbers aren’t as meaningful as the national number, because spree killings aren’t concentrated like that. The last spree killing was not in Virginia, and the next one probably won’t be either.

In short, what makes the massacre at VT, or any other spree killing, so vivid is that it happened all at once, all in one location. Availability bias makes us interpret such an event as indicative of a major problem. Any “solution” for spree killings – whether implementing tougher gun controls or replacing gun-free zones with concealed-carry permits – would have a negligible impact unless it also affected everyday, run-of-the-mill homicides.

This should go without saying, but I’ll say it anyway: none of this is meant to minimize the grief of the Virginia Tech community, or of the family and friends of the victims. It is simply meant to put the event into perspective.


Anonymous said...

Yes, there are lots of other ways to put the seemingly senseless slaughter at Virginia Tech into perspective. Just look at all the inequity and injustice all around you that you tolerate without the slightest outrage. Personally, I feel the equivalent of a crazed assasin's bullet everyday as I bear witness to all the evil that immoral people are committing.

I'm sure Don Imus only wishes that Cho acted a couple of days prior to his racially insensitivite outburst. His awful show might then have been salvaged. Thinking about your last post, perhaps God intervened to delay the VT killings by a few days to make sure of getting rid of that cretin Imus. The fact that 31 innocent people had to die to make that happen is statistically insignificant as you so rightly point out. We must always look at the bigger picture to keep things in perspective. I think it's careless & immoral not to.

Anonymous said...

Homicides are not all alike.

~Qualitatively~ the VA Tech incident is special for the same reason Columbine and the 2006 Amish school massacre and so on were qualitatively special -- they were random, involved children, were mass murders, and took place in settings customarily thought to be havens of safety. Granted, sprees like this are exceedingly rare, and should be put in perspective, but it also makes sense, on an emotional level, to find them uniquely scary and exceptional.

Anonymous said...

I would be interested to see what the effect of the 'Gun Free Zone' status of the VT campus had on the outcome of this tragedy. You may recall reading about another famous Whitman - when firing from atop the University of Texas Tower, civilians (including students) had grabbed their deer rifles and began firing back thereby reducing Charles Whitman's options to sniping out of water spouts. Otherwise, his spree may have gone on untrammeled for some time.
I'm not saying that more liberal gun ownership laws would have necessarily reduced the loss of life - just that it has in the past.