Undocumented immigrants reduce the rate of violent crime in the United States, according to a new study, despite immigrants struggling with many socioeconomic factors shared by people who are more likely to commit crimes.

University of Wisconsin–Madison sociology professor Michael Light undertook the comparison of undocumented immigration and violence in an effort to examine the relationship between two notable recent shifts in American society. His findings are published in the journal Criminology.

“Since 1990, the undocumented immigrant population in the United States has tripled. It’s part of the largest wave of immigration the country has ever experienced,” says Light. “In that same time, the violent crime rate has halved.”

And the impact of undocumented immigration — especially on public safety — remains a contentious topic of discussion in the United States.

“This is one of those rare areas everyone is talking about, but the conversations are occurring in a vacuum of data,” Light says. “A lot of research has looked at immigration and crime, but most of those conversations have been limited to the overall foreign-born population or the Latino foreign-born population, not the undocumented population.”

Light and Purdue University sociology graduate student Ty Miller used state-level immigration data from the Center for Migration Studies and the Pew Research Center spanning 1990 to 2014, comparing undocumented immigration rates to an index of violent crimes — homicide, rape, robbery and aggravated assault — kept by the FBI. They also examined the impact of undocumented immigration on violent victimization rates from the National Crime Victimization Survey.

All told, the researchers examined annual rates of migration and crime-related factors such as unemployment, age, gun availability and drug activity for each of the 50 states and Washington, D.C., over the course of 24 years — more than 1,000 discreet time periods with which to weigh the effect of undocumented immigration.

“The direction of the relationship is fairly clear,” says Light. “They’re all negative.”

More undocumented immigration meant less violent crime. According to the study, a 1 percent increase in the proportion of the population that is undocumented is associated with 49 fewer violent crimes per 100,000 people.