This diary is third in a series published by the Firearm Law and Policy group on the topic of defensive gun use. Part I reports on defensive gun use as described in the Center for Disease Control review of gun violence in America. Part II discusses the many difficulties in defining and determining a proper and legal defensive use of a gun. This Part III will review the well-known McDowall & Wiersema 1994 study that estimated the incidence of defensive gun use in America. Part IV will review another well-known study of defensive gun use: the 1995 study reported by Kleck & Gertz. Part V will compare the two studies and their methodologies.
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Introduction
According to the Center for Disease Control, America's premier institution of public health and safety, over 100,000 Americans suffer a gunshot injury every year, and every year, over 30,000 Americans die of their gunshot injuries. For this reason, and for others, many Americans conclude that gun ownership and gun use is highly dangerous, and gun sales and use should be limited and tightly controlled.
Guns are very popular in this country, and gun enthusiasts claim that guns contribute positively to the wider society. Chief among the benefits of gun ownership and use is safety and protection: a gun can be used defensively to prevent crime or stop a crime in progress, and guns help to protect and make safe the home and family. While acknowledging that guns injure and kill many, gun enthusiasts say that defensive gun use is beneficial overall and outweighs any negative impact of guns.
So accurately assessing the frequency of gun injuries and defensive gun uses (DGU) have become central to the debate about gun policy in the USA.
Accurately counting gunshot injuries and gunshot deaths is relatively easy. You simply count up the number of people injured and killed by bullets over a given period of time. Police and hospitals keep records of gunshot injuries and deaths, and every year, the Center for Disease Control collects those records and publishes a yearly tally of the total number of fatal and nonfatal gunshot injuries across the USA. This gives the counting of gunshot injuries an almost unassailable credibility: even the gun industry does not refute the accuracy of the yearly statistics on gunshot injuries.
Counting defensive gun uses is much more difficult. There is no public agency in America that keeps track of DGUs. For this reasons, the incidence of DGU is not counted and tallied every year, but instead must be estimated through surveys and polling – through empiric research. Unfortunately, to date the research on the incidence of DGU has yielded wildly inconsistent results, and some considerable controversy among public health researchers, criminologists, and the general public.
This series will review two of the most frequently cited studies of the incidence of DGU in the USA: the 1994 study authored by David McDowall, and the 1995 study authored by Gary Kleck. These two studies were chosen for review here because they represent the alpha and the omega of empiric research on DGU – both studies are well-know and widely cited in the scientific and lay literature, and these two studies present the high and the low ends of estimates of DGU. We will review the methodologies of these two studies to try and understand why they came up with such different results, even as they purport to measure the same thing.
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Study: The Incidence of Defensive Firearm Use by US Crime Victims, 1987 to 1990 (McDowall D., Wiersema B. American Journal of Public Health, 84:1982-1984; 1994)
Writing in the December 1994 issue of the American Journal of Public Health, principal investigator David McDowall, PhD and co-author Brian Wiersema used data from the National Crime Victimization Survey (NCVS) to estimate DGUs. They described the need and the purpose of the study in this way: "We were interested in the incidence of defense and the situations in which it occurs." They examined data from the years 1987 through 1990. They reported that during the years under examination, there were 143.9 million incidents of crime. During that period, there were 258,460 incidents of firearm resistance to crime, for an average of 64,615 DGUs every year. They reported that victims of crimes used guns defensively in 0.18% of all crimes, and in 0.83% of violent crimes. The study counted 50,262 self-defense gun uses by police in the line of duty during the study period. Removing these police DGU drops the yearly estimate of civilian DGUs to 51,959. McDowall concluded that DGU is rare in the USA. Dr. McDowall published a follow-up study in 1998 using data from the 1992 and 1994 waves of the NCVS, in which the estimate of yearly DGU was adjusted upwards to 116,000 (McDowall, D., C. Loftin, and B. Wiersema. Estimates of the Frequency of Firearm Self-Defense from the Redesigned National Crime Victimization Survey. Violence Research Group Discussion Paper 20; 1998. (unpublished report)).
The National Crime Victimization Study (NCVS)
The NCVS study (link) is an ongoing annual survey of crime victims done by the US Census Bureau on behalf of the Department of Justice – Bureau of Justice Statistics. The survey is conducted every year, as it has been since 1973. The purpose of the survey is to assess crime victims on the frequency, characteristics, and consequences of criminal acts in America. The NCVS is designed to assess a representative sample of over 59,000 US households, and collected data from over 116,000 non-institutionalized adults subjects (the study has been modified since 1990 to survey a smaller number of people and households). Sampled households are retained in the survey for three years, and are surveyed twice a year for the period they are retained in the study. The sample includes police officers and security guards who might use guns at their jobs. Being a Census Bureau survey, contact with interviewees is made through telephone and personal interview. The response rate for the survey was reported to be 95%.
Interviewees in the study are asked about incidents of rape, sexual assault, assault, robbery, theft, household burglary, and motor vehicle theft that occurred to them personally in the previous six months. Respondents who report an incidence of crime are then asked questions about self-defense:
“Was there anything you did or tried to do about the incident while it was going on?”
Responses from victims who answer they took action during the criminal attack are coded into one of 16 categories, including “attacked offender with gun; fired gun”, and “threatened offender with gun”. The interviewer continues to ask “anything else” until the crime victim reports no further actions taken. The survey follows these questions with an additional probe:
“Did you do anything (else) with the idea of protecting yourself or your property while the incident was going on?'
and affirmative responders are asked to detail their actions.
(Follow this
link to view the full study questionnaires)
For the purpose of estimating DGUs, the advantages of this study design are
1) the study is publicly funded;
2) the study is done by a government agency with extensive experience in conducting representative national surveys;
3) the large representative sample size;
4) the “representativeness” of the sample is maintained by making personal contact with households that do not respond to telephone contact;
4) the reliability of the responses is maintained by repeating interviews with the households every six months;
5) because interviews are conducted every 6 months, episodes of “telescoping*” can be identified and controlled;
6) a DGU is only counted in the setting of a criminal attack.
*"Telescoping" is the term given by researchers to a phenomenon whereby survey respondents mistakenly recall and include events that are outside of the period of time under investigation.
The disadvantages of this study design are:
1) the study is not specifically designed to measure DGUs;
2) the study does not track every type of crime;
3) the study does not ask every interviewee about episodes of DGU;
4) interviewees are not specifically asked about defending themselves with a gun;
5) follow-up studies have demonstrated that the incidence of assault (and especially assaults by relatives and non-strangers) in the NCVS is under-reported, and if crime is under-reported then so too will DGUs be under-reported;
6) respondents’ anonymity is not preserved, and some interviewees may therefore feel wary or unwilling to discuss gun use with federal government employees.
The Daily Kos Firearms Law and Policy group studies actions for reducing firearm deaths and injuries in a manner that is consistent with the current Supreme Court interpretation of the Second Amendment. We also cover the many positive aspects of gun ownership, including hunting, shooting sports, and self-defense.
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