Kleck has done numerous studies of the effects of guns on death and injury in crimes, on suicides, and gun accidents, the impact of gun control laws on rates of violence, the frequency and effectiveness of defensive gun use by crime victims, patterns of gun ownership, why people support gun control, and "the myth of big-time gun trafficking." In addition to his work on guns and violence, Kleck has done research concluding that increasing levels of punishment will not increase the deterrent effects of punishment, and that capital punishment does not have any measurable effect on homicide rates.
Kleck conducted a national survey in 1994 and, extrapolating from the 5,000 households surveyed, estimated that in 1993 there were approximately 2.5 million incidents of defensive gun use, compared to about 0.5 million gun crimes as estimated by the National Crime Victimization Survey. David Hemenway at the Harvard School of Public Health Injury Control Research Center, said that Kleck's estimates are difficult to reconcile with comparable crime statistics, are subject to a high degree of sampling error, and that "because of differences in coverage and potential response errors, what exactly these surveys measure remains uncertain; mere repetition does not eliminate bias." Kleck and Gertz responded to this criticism saying: "It is obvious to us that David Hemenway had no intention of producing a balanced, intellectually serious assessment of our estimates of defensive gun use. Instead, his critique serves the narrow political purpose of 'getting the estimate down,' for the sake of advancing the gun control cause." Kleck asserts errors in his critics' claims that his survey's estimates of defensive gun uses linked with specific crime types, or that involved a wounding of the offender, are implausibly large compared to estimates of the total numbers of such crimes. The total number of nonfatal gunshot woundings, whether medically treated or not, is unknown, and no meaningful estimates can be derived from his survey regarding defensive gun uses linked with specific crime types, or that involved wounding the offender, because the sample sizes are too small. The fact that some crime-specific estimates derived from the Kleck survey are implausibly large is at least partly a reflection of the small samples on which they are based - no more than 196 cases. Kleck states that his estimate of total defensive gun uses was based on nearly 5,000 cases. Thus, he argues, the implausible character of some estimates of small subsets of defensive gun uses is not a valid criticism of whether estimates of the total number of defensive gun uses are implausible or too high. Marvin Wolfgang, who was acknowledged in 1994 by the British Journal of Criminology as ″the most influential criminologist in the English-speaking world″, commented on Kleck's research concerning defensive gun use: A 1997 National Institute of Justice publication demonstrated that it is virtually impossible to reconcile Kleck's estimates and Kleck-like estimates to the amount of crime that actually occurs in the United States. Kleck, however, counter-argued that this conclusion was the product of logical errors and a mistake by the authors in which they made an inappropriate apples and oranges comparison.
