It wasn't long after the shooting of Congresswoman Gabrielle Giffords and 19 others in Tucson, Ariz., that speculation emerged about a possible connection between the shooting and the contemporary U.S. political environment.

In a news conference after the January 8 attack, which left six dead, Pima County sheriff Clarence Dupnik spoke out against inflammatory rhetoric and "the vitriol that comes out of certain mouths." Across social-media sites and in the mainstream press, numerous commentators noted that Giffords, an Arizona Democrat, had appeared on a list of legislators, each marked with crosshairs on a map, that former Alaska governor Sarah Palin's political action committee released in 2010. The target list identified 20 legislators from swing districts who had voted for health-care reform and who were up for election.

Giffords, 40, remains in critical condition, and her accused shooter, Jared Lee Loughner, 22, is in custody. Loughner's motives remain unclear, and no coherent political link has emerged. But even in instances where consumption of violent media has been cited as a factor in crime, researchers say it is usually only one factor among many.

"The problem in any specific case is that you can't really know for sure whether an incident would have happened had not there been, say, a lot of media violence exposure," says psychologist Craig Anderson, director of the Center for the Study of Violence at Iowa State University. "In this particular case, we can't really know whether such shootings would have taken place had there not been this recent history of fairly nasty political exchanges in the press."

Anderson has authored several studies on the effects of violence in television and video games and contributed to a 2009 policy statement on media violence from the American Academy of Pediatrics. "The evidence is now clear and convincing," the report asserted: "media violence is one of the causal factors of real-life violence and aggression."

But that causal factor does not operate in a vacuum. "Extreme acts of violence such as this shooting never occur with only one risk factor being present," Anderson says. Among the common risk factors: gender, age, a history of childhood abuse, a variety of environmental and genetic factors—and, in many cases, access to firearms. "The key point that I try to make to people is that multiple risk factors are in play," Anderson says. "So it's a leap to try to claim that any one risk factor was key."

Some researchers, such as psychologist Christopher Ferguson of Texas A&M International University, dispute the causal relationship between viewing violent media and acting out violently in real life. "There is still some debate about whether it is a risk factor, and I would argue that it's not," Ferguson says of video games, noting that violent crimes among juveniles have been on the decline even as games have increased in both prevalence and graphicness.

Similarly, studies by Ferguson and by other researchers, such as economist Todd Kendall, have found a decrease in rates of rape that coincides with increased availability of pornography. "Once again you see this sort of inverse relationship across not just in the U.S. but in other countries as well between pornography consumption and the actual rates of sexual violence," Ferguson says. That does not mean that video games prevent violence, or that pornography curbs sexual crime, but it does highlight the difficulty in establishing a casual relationship between any one medium and a group's behavior, let alone the actions of an individual.

In the case of Loughner, we may never know if the fraught political climate in the U.S. had anything to do with his actions in Tucson. "It's irresponsible in my opinion to start blaming anything until we know more about this individual," Ferguson says. "I think we're really rushing to judgment, and that's not to say that I like this kind of political speech. I find it atrocious, like everybody else."

Adds Anderson: "I think it would be fair to say that when political discourse gets more and more strident, and when there are images portrayed on the Web where you have a scope sight as part of your attack on your political opponent, that isn't helpful. I think that's safe to say. But whether or not it plays any major causal role in any given case, it's just impossible to say."