There is an apartment search site called “Zumper.” Zumper has come up with a very smart marketing ploy, which is something they call a “National Rent Report.” The “National Rent Report” reports on how much rent is, nationally, in a bunch of different cities and neighborhoods.

People like to know how much other people are paying for things, compared to how much they are paying, and they like to get updates about the course of neighborhood change, and that sort of thing, so the “National Rent Report” gets picked up by media outlets all over the place.

Most recently, I saw it on Curbed, which reported that, according to the “National Rent Report,” the median one-bedroom apartment in Chicago goes for $1,780. (I don’t mean to pick on Curbed, which I read constantly, is generally excellent, and far from the only outlet to pick up the “National Rent Report.”)

The median one-bedroom apartment in Chicago does not go for $1,780.

I could go into any number of reasons how I know that’s true. But the simplest is to look at Zumper’s own numbers for Chicago:

Recall that the definition of “median” is “the point at which there are an equal number of items above and below.” Now look at this list. According to Zumper itself, there are only five neighborhoods in the entire city of Chicago where the median rent is above $1,780. If the city’s median rent as a whole is $1,780, then one of these things must be true:

1. There must only be ten neighborhoods in all of Chicago of roughly equal size, or

2. There can be more than ten neighborhoods, but half of all the one-bedroom apartments in the city must be located in just five neighborhoods.

Neither one of these things is true. Rather, the issue is almost certainly that half of Zumper’s listings are in one of those five neighborhoods, because their listings are very, very concentrated in high-end apartments.

But that makes their listings completely worthless for determining the actual median rent for the rest of us, who live in a world that is not bounded by Zumper’s database.

Which makes the “National Rent Report” completely worthless.

Let’s all stop writing about it.