Spend enough time in New York City, and you'll likely spot a rat. Maybe it'll be scampering along the subway tracks. Maybe it will run right across your path—even your foot. New Yorkers like to point out that there are as many rats in New York as there are people (8.4 million); over the summer, the New York Post reported that rats could outnumber people two to one.
This common knowledge, however, turns out to be a gross overestimate. While vermin are indeed populous, they're not that populous, found statistician Jonathan Auerbach. In fact, the real ratio is closer to four-to-one, with humans winning.
Auerbach's calculations aren't precise, but they're probably the truest-to-reality figures we've got. The problem, NPR writes, is that the typical method for estimating an animal population involves capturing, tagging and releasing those animals. Researchers then capturing them again to see how many show up with the tags, and statistics helps them extrapolate population sizes from there. But this would technically count as releasing rodents into NYC, a practice that the Department of Health and Mental Hygiene immediately turned down, NPR writes.
So instead of gathering direct data from the field, Auerbach turned to an indirect measurement: rat sightings reported to the city's 311 hotline. Using the number of city property lots, the number of rat reports that came from each of those 842,000 subsections and what we know about the number of rats that tend to occupy a single colony, Auerbach was able to extrapolate the population number as a whole, NPR writes. The value he arrived at—about 2 million—is significantly lower than the 8.4 million that most people assume occupy the sewers, subways and streets of New York.
Perhaps equally surprising for some New Yorkers is the recent announcement that NYC is not, in fact, the most rat-infested metropolis in the U.S. According to data released by the pest control company Orkin, Chicago, Los Angeles and Washington, D.C., are all rattier places than New York City. Whether those rodent populations exceed 8 million, however, is unknown.