Researching the link between gun prevalence and crime is inherently tricky. When society itself is your laboratory, it's almost impossible to properly account for confounding variables that might skew the results. All sorts of factors, ranging from unemployment to alcohol use, can get in the way.

Acknowledging the limitations of current research on the link between gun ownership and crime, Florida State University criminologist Gary Kleck sorted through dozens of studies to first separate the best from the worst, and then determine what the strongest studies tell us. His efforts were recently published in the Journal of Criminal Justice.

"All research is flawed, and all bodies of research are incomplete," Kleck noted, "but that does not mean we cannot distinguish the less flawed work from the more flawed, and draw tentative conclusions based on the best available research conducted so far."

Kleck included 41 studies that examined the association between measured gun levels and crime rate in his analysis, then used three specific criteria to gauge the strength of the studies.

First, he looked for a validated measure of gun ownership. In-depth surveys and percent of suicides with guns were two of the few acceptable measures. Second, he checked to see if confounding variables were properly controlled for and how many were included. Third, he checked to see whether the researchers used procedures that would rule out reverse causality, i.e. whether crime rates actually caused gun ownership to increase. (Past studies have shown that when crime rises in an area, gun ownership often increases, likely for purposes of self-defense.)

In all, the 41 studies produced 90 findings on gun ownership and various crime rates. Of these, 64% found no statistically significant positive affect between gun ownership and crime. However, 52% did identify a link between gun ownership and homicide.

When Kleck applied his three methodological criteria (valid measure of gun ownership, causality procedures, controlled for >5 confounding variables) to the studies, he found that the more criteria they met, the more likely they were to show no link between gun ownership and crime. The reversal was particularly noticeable for homicide. While 65% of the studies that met none of the criteria found a link between gun ownership and homicide, the three studies that met all of the criteria did not.

"The overall pattern is very clear – the more methodologically adequate research is, the less likely it is to support the more guns-more crime hypothesis," Kleck remarked.

Kleck offered two explanations for the finding.

"The most likely explanation is that most guns are possessed by noncriminals whose only involvement in crime is as victims, and defensive gun use by crime victims is both common and effective in preventing the offender from injuring the victim."

Kleck has been researching crime for over thirty years. In the past, he's published studies showing that capital punishment has no effect on homicide rates and that victims who resist rape attempts are more likely to escape and no more likely to suffer worse injuries. He's best known for the hotly debated National Self-Defense Survey published in 1994, which estimated that there were 2.5 million incidents of defensive gun use in 1993.

Kleck's current review indirectly conflicts with a widely cited review published last year by researchers from the University of California. They found that access to firearms in the home is linked to a 3.2x higher risk of suicide and a 2.0x higher risk of homicide.

Understandably, scientists have had a difficult time nailing down a correlation between gun prevalence and crime. In all likelihood, the relationship is not as simple as politicians and ideologues would like us to believe.

Source: Gary Kleck. "The Impact of Gun Ownership Rates on Crime Rates: A Methodological Review of the Evidence." Journal of Criminal Justice 43 (1): 40-48. Jan-Feb 2015. doi:10.1016/j.jcrimjus.2014.12.002

(AP photo)