Follow the Evidence

Watching CSI recently, I suddenly found myself wondering if the vast number of murders we see on the show is overstating the actual murder rate in Las Vegas. So I decided to research it.

There are 22 episodes of CSI every season. The vast majority of episodes cover two murders, though a few episodes do only have one murder (more this season than in the past). Very occasionally, they investigate a crime other than murder -- a theft, or something that turns out to be a suicide or accidental death. Just as occasionally, though, they have episodes that cover three or more murders. And also occasionally, they'll cover a murder that's not in the city proper. So, doing a rough guestimate of how that all balances out, let's say that CSI depicts 1.5 Las Vegas murders per episode, or 33 per season.

Now comes the Googling. It turns out that finding the actual number of murders in one year in any U.S. city was not as easy to do as I would have guessed. No one wants to talk about actual numbers. Instead, the stat is always provided "per capita." I suppose you'd expect this, lest populous cities like New York and Chicago look worse than they probably are. Anyway, I was able to get the "murder rate per 100,000 citizens" for Las Vegas in 2003, and then found the actual population of Las Vegas. Some quick multiplication, and I determined there were 57 murders in Las Vegas that year.

So, 57 actual murders in one year, 33 murders in a year of CSI.

Now there are a few ways you can choose to interpret this -- and they are all rather humorous if you ask me. At the simplest level, you can just look at the raw numbers and see that over half the murders in Las Vegas are depicted on the show. That's pretty extreme.

But you can also take into account that the good folks at CSI work just one shift. (Notwithstanding the season where the team was split up.) Even if you assume their shift is the "busy one" (and it tends to be the night shift, where one would figure that indeed most murders happen), they're finding more than half the bodies. From that, you can pretty much conclude that we're being shown every murder that takes place when these people are on duty.

However, there's also a third way you can look at this. CSI often makes references to the date, and they do a pretty good job of it being the actual date (or very close to the date) when the episode first airs. In other words, time in the real world is passing at the same rate as time in the CSI world; this isn't like 24 or Lost where the passage of time on the show is slower than the rate at which episodes air. Once you look at it from that perspective, you have to go back and realize that in real life, 57 murders occur in 52 weeks -- just barely more than 1 a week. But CSI is showing us just 22 particular weeks in the year, and in each we're getting about 1.5 bodies. So, in the world of CSI, about 78 murders are happening each year in Las Vegas -- about 20 more than in real life.

Not that I think this distortion of reality is hurting their tourism industry.

I've geeked out enough now. Someone else can run the math on New York and Miami.