Playing violent video games is linked to increases in aggression and decreases in sensitivity to aggression, according to a review by the American Psychological Association (APA) of recent research. The review indicated that there is “insufficient evidence” about whether playing violent video games can also lead to criminal violence or delinquency, the APA announced today.

The review comes in a 49-page report from the APA Task Force on Violent Media, which the APA established in January 2013 to review scientific literature published between 2005 and 2013 about the effects of violent video games.

“The research demonstrates a consistent relation between violent video game use and increases in aggressive behavior, aggressive cognitions and aggressive affect, and decreases in prosocial behavior, empathy and sensitivity to aggression,” the report concludes. The Entertainment Software Association refuted the report in a statement to Polygon, pointing out that the Supreme Court previously dismissed the supposed link.

There isn’t enough evidence of a potential link between playing violent games and committing acts of criminal violence, according to the report, because “very limited research” exists on that topic, said Mark Appelbaum, PhD, chair of the APA Task Force, in a press release.

The report notes that “no single risk factor consistently leads a person to act aggressively or violently. Rather, it is the accumulation of risk factors that tends to lead to aggressive or violent behavior.” Playing violent video games is one such risk factor, the report says.

Based on the report, the APA has adopted a new set of policies and recommendations that replaces its 2005 “Resolution on Violence in Video Games and Interactive Media.”

In the new document, simply called “Resolution on Violent Video Games,” the APA “strongly encourages” the ESRB to update its video game rating system “to reflect the levels and characteristics of violence in games, in addition to the current global ratings.” The APA will also endorse the development of “rigorously tested interventions” that educate children and families about the effects of playing violent games, and will support further research into the field.

Additional research is necessary to fill gaps in knowledge of the consequences of playing violent video games, according to the report. The APA Task Force identified limitations of the existing body of research such as the effects of playing violent games on children under the age of 10 — most studies have focused on adolescents and adults — and whether the effects differ between male and female individuals.

Challenging the APA Task Force

Appelbaum acknowledged “some variation among the individual studies,” but said that “a strong and consistent general pattern has emerged from many years of research that provides confidence in our general conclusions.”

But the Entertainment Software Association, the trade body representing the U.S. video game industry, disagrees with the APA Task Force’s report. The organization slammed the report in a statement to Polygon, saying, “Considering the APA’s long-standing bias against and attacks on video games, this slanted report is not surprising. Numerous medical professionals, researchers, and courts all debunk the fundamental thesis of their argument.”

The ESA went on to cite the Supreme Court’s opinion in Brown v. EMA, the 2011 case in which the court decided a California law that criminalized the sale of violent video games to minors was unconstitutional.

“In tearing down similar faulty research, the U.S. Supreme Court specifically ruled that ‘psychological studies purporting to show a connection between exposure to violent video games and harmful effects on children do not prove that such exposure causes minors to act aggressively.’ We could not state it better,” the ESA said.

Regarding the ESA’s charges of a “long-standing bias” against video games at the APA, it’s worth examining the APA Task Force on Violent Media more closely.

The APA Task Force was created in January 2013, the same month President Barack Obama suggested further research from the Centers for Disease Control and Prevention into the potential links between video games, “media images” and violence. That call to action followed the December 2012 mass shooting at Sandy Hook Elementary School in Newtown, Connecticut, in which 20 students and six adult staff members were killed.

In September 2013, a group of nearly 230 academics, researchers and psychologists signed a letter expressing concerns about the APA Task Force’s review process. The APA’s original 2005 resolution came to “several strong conclusions on the basis of inconsistent or weak evidence,” according to the signatories of the letter. They continued, “Research subsequent to that 2005 statement has provided even stronger evidence that some of the assertions in it cannot be supported.”

Two of the seven members of the APA Task Force, Kenneth Dodge, PhD and Sherry Hamby, PhD, endorsed an amicus curiae brief submitted in favor of upholding the California law in the Brown v. EMA case. The brief came from now-disgraced California state Sen. Leland Yee, a well-known crusader against violent video games.

The APA Task Force’s review also doesn’t include the latest research on violent video games, since the Task Force only examined studies published until mid-2013. A 2014 study led by Matthew Grizzard at the University at Buffalo indicated that practicing immoral behavior in a virtual environment — such as killing someone in a violent video game — could actually lead to an increase in prosocial behavior. Contrary to the APA Task Force’s report, Grizzard’s research found that players would become more sensitive to the moral codes they were violating in the game.