Let's Clear This Up — In New York City, There's Only 1 Rat For Every 4 People

Transcript

AUDIE CORNISH, HOST:

Few things spark revulsion like rats.

(SOUNDBITE OF FILM, "INDIANA JONES AND THE LAST CRUSADE")

HARRISON FORD: (As Indiana Jones) Oh, rats.

CORNISH: Most people, including Indiana Jones, find them filthy, mean - just nasty. And if you live in a big city, you have likely crossed paths with rats many times. They seem to be everywhere. So it's easy to accept this idea. New York City has as many rats as people. But is that true?

JONATHAN AUERBACH: Very unlikely.

CORNISH: That our rat myth debunker, Jonathan Auerbach. He's here to talk about how many rats are likely to actually live in New York. What's that number, Jonathan?

AUERBACH: Less than two million.

CORNISH: Jonathan Auerbach is a PhD student in statistics at Colombia University, and he's authored an award-winning study tackling this, turns out unfounded, belief. And first of all, where did this idea come from? I mean, how many rats do people think are in New York City?

AUERBACH: People think there's around eight million, but no one's quite sure where the statistic comes from. Robert Sullivan, who is a rat journalist, attributes it to W.R. Bolter (ph) a man who was writing at the turn of the century.

CORNISH: And at that time he kind of came up with this idea of there being one rat per acre in a community, right?

AUERBACH: Yeah. There happened to be the same number of acres in England, where he was from, as people in England. So he drew the one rat per person connection.

CORNISH: And we talked about that a eight million number being a kind of rumor or urban myth, but what has the city been saying?

AUERBACH: The city says a whole bunch of things depending on who you ask. You know, it's actually funny. I was talking to someone who's an exterminator. And he was under the belief that there were trillions - I mean just giant colonies of rats.

CORNISH: Trillions. (Laughter).

AUERBACH: Trillions - some unfathomable number. And I guess if your job is to get them day in and day out, it seems like there's this unfathomable number. And then I talked to people who worked more with data, and they thought less than eight million. And then other people think eight million. And I think the lesson here is that when nobody knows, you know, everyone's got their own personal assessment based on their own anecdotal evidence.

CORNISH: To be clear, you're a numbers guy. I mean, you use data from the 3-1-1 service phone number. This is the number people call in New York City for non-emergencies. And so people actually call in and say hey, I saw a rat.

AUERBACH: Mhm.

CORNISH: And what did you find in the data?

AUERBACH: That the data exhibits patterns that are inconsistent with the idea that there are eight million hanging around. The actual number is likely to be less than two million.

CORNISH: But New Yorkers, like many city dwellers I can imagine, might be jaded, right? I mean, maybe they're underreporting how many rats that they see.

AUERBACH: So the assumption in this paper was that within a specific neighborhood, people call in consistent manners. It could be that only 90 percent of the people who see a rat think about calling and 10 percent of them actually call, and then 2 percent have the patience to stay on the line in order to have their call registered.

CORNISH: Right, that's half the battle, right - sticking it out over the service.

(LAUGHTER)

CORNISH: And have you had any pushback since you kind of put out a proper number?

AUERBACH: If I had, you know, come out and said I think the agency is doing a terrible job, and they're putting out B.S. numbers, I think there probably would have been pushback. But for the most part, I think I'm saying if we're going to be using numbers like these in order to evaluate policy, let's try to come up with some numbers that are backed by data.

CORNISH: So why do you think people are so attached to this idea, right - that there would be as many rats as people?

AUERBACH: I think people like the one rat per person statistic because everyone has seen a rat.

CORNISH: So this - (laughter) so anecdotally, if I've seen one, then people count that as their one rat, right - their rat soul mate?

AUERBACH: Right. It falls apart when you consider other issues - you know, bike thefts. Maybe everyone knows someone who has had their bike stolen. Clearly there aren't eight million people running around stealing bikes.

CORNISH: Jonathan Auerbach, thanks so much for talking with us.

AUERBACH: Thank you.

CORNISH: That's Jonathan Auerbach. His survey is called "Does New York City Really Have As Many Rats As People?" It won the Young Statisticians Writing Award. Transcript provided by NPR, Copyright NPR.