There are approximately two million defensive gun uses (DGU's) per year by law abiding citizens. That was one of the findings in a national survey conducted by Gary Kleck, a Florida State University criminologist in 1993. Prior to Dr. Kleck's survey, thirteen other surveys indicated a range of between 800,000 to 2.5 million DGU's annually. However these surveys each had their flaws which prompted Dr. Kleck to conduct his own study specifically tailored to estimate the number of DGU's annually.

Subsequent to Kleck's study, the Department of Justice sponsored a survey in 1994 titled, Guns in America: National Survey on Private Ownership and Use of Firearms (text, PDF). Using a smaller sample size than Kleck's, this survey estimated 1.5 million DGU's annually.

There is one study, the National Crime Victimization Survey (NCVS), which in 1993, estimated 108,000 DGU's annually. Why the huge discrepancy between this survey and fourteen others?

Dr. Kleck's Answer
Why is the NCVS an unacceptable estimate of annual DGU's? Dr. Kleck states, "Equally important, those who take the NCVS-based estimates seriously have consistently ignored the most pronounced limitations of the NCVS for estimating DGU frequency. The NCVS is a non-anonymous national survey conducted by a branch of the federal government, the U.S. Bureau of the Census. Interviewers identify themselves to respondents as federal government employees, even displaying, in face-to-face contacts, an identification card with a badge. Respondents are told that the interviews are being conducted on behalf of the U.S. Department of Justice, the law enforcement branch of the federal government. As a preliminary to asking questions about crime victimization experiences, interviewers establish the address, telephone number, and full names of all occupants, age twelve and over, in each household they contact. In short, it is made very clear to respondents that they are, in effect, speaking to a law enforcement arm of the federal government, whose employees know exactly who the respondents and their family members are, where they live, and how they can be recontacted."

"It is not hard for gun-using victims interviewed in the NCVS to withhold information about their use of a gun, especially since they are never directly asked whether they used a gun for self-protection. They are asked only general questions about whether they did anything to protect themselves. In short, respondents are merely give the opportunity to volunteer the information that they have used a gun defensively. All it takes for a respondents to conceal a DGU is to simply refrain from mentioning it, i.e., to leave it out of what may be an otherwise accurate and complete account of the crime incident."

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