It’s difficult to measure the size of an economy which, on paper, doesn’t exist. Weapons trafficking, drug trafficking, and sex trafficking all comprise a hidden, underground market which, away from the eyes of regulators, law enforcement, and economists, can be difficult to comprehend, let alone measure. And because there is so little in the way of data surrounding these underground economies, attempts at controlling them can feel a little like fighting blind: there’s no real way to ascertain the size, shape, or nature of the beast.

But earlier this year, the Urban Institute, a group made up of independent scholars whose aim is to provide scholarly insight into issues affecting urban areas, released an extensive report with the goal of tracking the size of the underground commercial sex economy, as well as trends within the industry that might help aid law enforcement officials and legislators alike. It’s a ground-breaking study.

The report is important for legislators and law enforcement because, as the study notes, the underground sex economy is one that is constantly adapting and responding to police and law enforcement tactics. Law enforcement moves in one direction, and those in the industry move in another. It’s easy to see why the problems created by the underground sex economy can often seem so insurmountable.

Meredith Dank, the report’s lead author, says that the study is “the first of its kind to look in-depth and create a road map of the commercial sex economy — from point of entry to reasons to stay within it, and what business and operations structure looks like,” she said in an interview with the New York Times. Previously, she said, “we’d hear numbers from law enforcement and advocacy groups. But there was never any empirical rigor that was used to estimate its size.”