There may be 8 million stories in the Big Apple, but one of them — that New York City is home to 8 million rats, or one for every human resident — is probably a tall tale, according to research by a Columbia University statistician.
In truth, the city’s rat population is probably closer to 2 million, said Jonathan Auerbach, who wrote an essay on the subject for a magazine.
The urban lore that there are as many rats as citizens dates back at least a century, Auerbach says. It may have endured in part because reliably estimating the city’s rat population is difficult even though the creatures are hardly invisible, as most New Yorkers who see them skittering about the subway tracks or hear them rustling through trash piles will attest.
“Animals are terrible survey respondents,” he wrote in the article, which was the winning entry in a young statisticians competition by London’s Royal Statistical Society.
Auerbach’s initial plan was to capture a random sample of rats, marking them, releasing them, and then capturing another random sample of rats.
But the city’s health department, which is responsible for dealing with rats, was not enthralled with the idea. Instead, Auerbach used complaints from the public about rat sightings, which the city tracks and publishes online. Combining the data with a number of assumptions, he was able to extrapolate the number of rat-occupied lots to about 40,500 across the city, or less than 5 percent of the total.
If each inhabited lot is home to a colony of 50 rats, that means there are about 2 million rats in the city.
The health department called the findings “interesting,” but said there was simply no valid method for counting any large city’s rat population.