As the federal government ramped up its efforts to fight human trafficking in the early 2000s, a key law passed by Congress in 2005 mandated that the Justice Department carry out “comprehensive research and statistical review and analysis of severe forms of trafficking in persons” every two years, to determine the depth of the problem in the United States.

But only one study was ever done, in 2009, and none since. Experts say no hard numbers exist on the number of victims, or traffickers. So on Thursday, Sen. Josh Hawley (R-Mo.) introduced a bill basically reiterating the wording of the Trafficking Victims Protection Reauthorization Act of 2005, while adding an accounting of trafficking victims. He said he would press Congress to appropriate the money to make the survey happen. Experts in human trafficking said the information is urgently needed to understand the breadth of the problem, to learn how traffickers operate and how to stop them.

“I think people are going to be shocked to learn we haven’t done a comprehensive national study,” Hawley said. “It’s important that we know the scope of the problem, and it’s more than a problem, it’s an epidemic. The first step is getting to the scope of the problem.”

Kevin Malone, president of the U.S. Institute Against Human Trafficking, said studies to capture the scope of trafficking “would be a tremendous help because a lot of people don’t believe the problem exists. A lot of times, the pushback we get is, ‘Where’s the data? Where’s the info?’ We’re out in the field, we can put numbers together on Los Angeles, or Tampa, and we realistically think 100,000 kids are being bought and sold in this country every day. But until we have the data, it’s almost like we need to prove it.”

Malone said definitive information on how many men, women and children are being sold or held against their will would be “almost like a game-changer because we’d like something else to point to besides what we know from the street.”

The trafficking act currently calls for two studies. The first addresses the estimated number and demographic characteristics of perpetrators of all types of trafficking, which could include forced labor, and the number of trafficking-related criminal cases. Hawley’s bill would require estimates on the numbers and demographics of victims.

The second study is specific to sex trafficking and seeks not only the number and types of perpetrators, but also the estimated dollar value of the commercial sex economy and the number of related criminal investigations.

“You don’t need extreme precision,” said Michael Shively, senior adviser to the National Center on Sexual Exploitation and a former contractor for the National Institute of Justice, the research arm of the Justice Department. “But if you’re talking about thousands of victims, or hundreds of thousands, or a million, that matters. How many victims? How many buyers?”

And, Shively added, “This is about more than just a number. There are nuances to it. The regional differences of the trafficking, the economic backgrounds of those being trafficked.” Knowing where the problems are most acute can help focus resources on those areas, Shively said.

Shively said a number of smaller human-trafficking studies had been funded over the years, but nothing on a national scale. Shively worked on one study in a Midwestern county where researchers spent two weeks in the county jail, two weeks in shelters and two weeks in hospitals, and found that about 7 percent of those interviewed were trafficking victims. “That extrapolated to 7,300 victims in the county,” Shively said, “and that’s probably conservative,” because the study used the definition of trafficking as those who are held by force. The study also found that virtually all of the victims had contact with a social service agency at some point, but many had not gotten the necessary help.

Hawley, the former attorney general of Missouri, said law enforcement officials are accustomed to having crime statistics and other analytic data to address problems in their community. But those fighting sex trafficking don’t have that data.

“I think this data will tell us who the victims are,” Hawley said, “who’s at risk of being victimized. What is it that makes them victimizable? Who are the perpetrators? What are their methods? We need to know about what the traffickers do, so we can liberate victims from this modern-day slavery and cut the bad guys off at the knees.”