For the past few years, campaigns against human sex trafficking have swelled in the days before the Super Bowl, largely because of the persistence of a claim that it’s the largest sex trafficking event in the country.

Sen. John Cornyn, R-Texas, who has been pushing anti-human trafficking legislation through Congress, repeated this at a Jan. 27 news conference.

"While most Americans are going to be getting prepared for the Seahawks and the Patriots to tee off in the Super Bowl," Cornyn said, "the dirty little secret is that the Super Bowl actually (has) one of the highest levels of human sex trafficking activity of any event in the country."

Cornyn’s staff clarified that he was not saying human trafficking surges nationally on Super Bowl Sunday. He meant that it surges in the region where the Super Bowl takes place and in the days surrounding the event. (This year, it’s Feb. 1 in Phoenix.)

But as it turns out, there is very little empirical evidence that speaks to this oft-repeated claim -- even though there is some recent academic research on the topic. While there are news reports and anecdotal examples of sting operations in Super Bowl host cities, comparisons to the rest of the year are rare, making it hard to know whether there’s a Super Bowl spike.

The latest evidence

We spoke with Dominique Roe-Sepowitz, a social work professor at Arizona State University who is leading the latest academic research on sex trafficking around the Super Bowl. Her research intends to discover whether or not there is an increase in sex-trafficking events surrounding the Super Bowl and to further understand sex trafficking trends.

(Sex trafficking is -- as defined by the Trafficking Victim Protection Act of 2000 -- a circumstance "in which a commercial sex act is induced by force, fraud, or coercion, or in which the person induced to perform such act has not attained 18 years of age.")

Roe-Sepowitz’s 2014 research used online escort ads to compare supply and demand for trafficking victims in New York City -- where the 2014 Super Bowl took place -- and used Phoenix as a control. During this weekend’s Super Bowl, they are looking at the same two cities and will publish a report in the coming weeks.

Last year, they reviewed online commercial sex ads in the New York and Phoenix metropolitan areas in the days leading up to and following the game. Out of nearly 1,000 ads in New York, 84 percent indicated possible sex trafficking. Among more than 1,300 ads in Phoenix, 80 percent indicated possible sex trafficking.

Roe-Sepowitz said that so far, the research does not show correlation between the Super Bowl and higher levels of sex trafficking activity.

They found some evidence of "victim movement and marketing trends that tend to correspond with the build up towards the Super Bowl" -- traffickers responding to the influx of thousands of men with money to spend. But they did not find that the level of activity was necessarily higher than other weeks out of the year.

On the other hand, increased public attention on trafficking around the Super Bowl might mean that the frequency is lower than it would be otherwise.

In all, this research does not conclusively prove one way or another that the Super Bowl is the largest event for sex-trafficking in the country.

Other debunkings

Some advocacy groups have tried to debunk the rumor, too.

Around the time of the 2014 Super Bowl, leaders from the Polaris Project -- an advocacy organization -- wrote a column in the Huffington Post, in which they acknowledged that the evidence for a spike in trafficking around the Super Bowl is slim. And the idea detracts from the fact that trafficking occurs year-round.

The Global Alliance Against Trafficking in Women, an advocacy group, published an extensive report on sex trafficking and the major sports events, including the Super Bowl, in 2011.

"The hype around large sporting events and increases in trafficking for prostitution is often based on misinformation, poor data and a tendency to sensationalize," the report says. "On various occasions, politicians have uncritically repeated this claim, despite the fact that numerous researchers, anti-trafficking experts, and non-governmental organisations (NGOs) have stated that there is no evidence of a link between large sporting events and trafficking for prostitution."

Cornyn’s staff sent us links to several news articles that they said indicated a spike in human trafficking around the Super Bowl. For example, the New York Attorney General ’s office had evidence that a prostitution ring offered special discounted "party packs" around the Super Bowl -- but those arrested were not charged with human trafficking (as opposed to prostitution).

Another article that Cornyn’s staff sent quotes Sen. Amy Klobuchar, D-Minn., who has worked with Cornyn on sex-trafficking legislation, saying: "During the Dallas Super Bowl in 2011 there was a 300 percent increase in the Internet ads regarding sex trafficking." Our friends at the Washington Post’s Fact Checker checked this claim and gave it their worst rating in terms of accuracy -- four Pinocchios.

Klobuchar was (incorrectly) citing an informal study out of the Texas-based Traffick911 . That study found a 172 percent spike in Internet ads for female escorts in the three weeks leading up to the Dallas Super Bowl. But that study does not specify that these posts indicated sex trafficking, rather than prostitution, and there’s no comparison to prior Super Bowls or trends in escort service posts at other times of the year in Dallas.

Cornyn’s staff also sent articles that included estimates of trafficking victims in areas around the Super Bowl host city in past years -- such as for those trafficked in the Miami area for the Super Bowl there in 2010. But there’s no way of knowing with certainty whether this is a spike, because we don’t have figures from the rest of the year to compare.

Our ruling

Cornyn said that the Super Bowl has "one of the highest levels of human sex trafficking activity of any event in the country."

There’s very little evidence to support this persistent claim. It’s certainly possible that a Super Bowl host city might attract more sex trafficking during the event than it would at other points in the year given the rapid arrival of many thousands of visitors with money to spend. But there’s no empirical evidence to prove it.

We rate his claim Mostly False.