The CPSTF finding is based on evidence from a systematic review of 4 studies (search period 1979 - March 2001). The review was conducted on behalf of the CPSTF by a team of specialists in systematic review methods, and in research, practice, and policy related to violence prevention.
Detailed results from the systematic review are available in the CPSTF finding [PDF - 132 KB].
Four studies were included in the systematic review.
- Two studies that evaluated the effect of felony conviction restrictions found favorable effects, though some of the effects were attributed to waiting periods rather than restrictions on acquisition.
- Studies that considered other restrictions showed favorable or mixed effects, but they were not statistically significant.
An economic review of this intervention was not conducted because the CPSTF did not have enough information to determine if the intervention works.
Applicability of this intervention across different settings and populations was not assessed because the CPSTF did not have enough information to determine if the intervention works.
The CPSTF identified several areas that have limited information. Additional research and evaluation could help fill remaining gaps in the evidence base. (What are evidence gaps?)
Research Issues Specific to Restrictions on Firearm Acquisition
- Examine the effects of restriction requirements in the secondary market (gun shows, private sales).
- Assess the proportion of firearm-related crimes committed by people in each of the prohibited categories.
- Examine the effect of specific restrictions on violence by populations to whom the restrictions apply (e.g., felons, drug abusers, or those adjudicated “mental defective”).
General Research Issues
The following outlines evidence gaps for these reviews of firearm laws: Bans on Specified Firearms or Ammunition; Restrictions on Firearm Acquisition; Waiting Periods for Firearm Acquisition; Firearm Registration and Licensing of Firearm Owners; "Shall issue" Concealed Weapons Carry Laws; Child Access Prevention (CAP) Laws; Zero Tolerance of Firearms in Schools; Combinations of Firearms Laws
Additional high-quality research is required to determine whether a relationship exists between firearms laws and violent outcomes. Below are areas for further potential study.
Violent Outcome Data Sources
It was noted at the outset of this article and in the assessments of specific laws that multiple problems exist with the available data on outcomes used in studies of firearms laws. Much remains to be done to improve the recording of events and accessibility of the relevant data. Improvements would allow better evaluation of the effects of firearms laws as well as improvements in understanding of other aspects of violence and injury. These include:
- Reporting systems for individual criminal and violent events and details of their circumstances
- More detailed data on the location and perpetration of the crime;
- More detailed data on agents in unintentional firearm-related injuries, linked to information on both the victim and the storage conditions of firearms involved;
- More detailed information on firearms used in crimes (e.g., type of firearm used, whether the firearm was carried legally, was registered, how it was acquired, and whether the owner was licensed)
- More statistics relevant to changes in behaviors that can be attributed to laws (e.g., the numbers of concealed carry permits issued, or changes in safe storage practices).
Measurement of Exposure: What Laws are in Place, and Where?
- Classification: There have been disputes about which states have which types of laws. Misclassification of state laws and their dates of implementation hinders firearms law research. Some differences among states in the effects of laws may be attributable to differences among states in provisions of the law, for example, their requirements, penalties, or the presence of other laws. A recent analysis of firearms laws (Vernick & Hepburn, 2003) may help to resolve some of these issues for researchers by providing a recent, systematic, and detailed analysis of major federal, state, and local firearms laws.
- Implementation and enforcement: As with any intervention, the degree of implementation may affect the intervention’s effectiveness. Data on implementation have typically not been included in the evaluation of firearms laws. How do the intensity and visibility of law enforcement differ among jurisdictions, and how do they affect the law’s effectiveness?
- Publicity and awareness of laws: Knowledge about laws may be one means by which they become effective. If deterrence is a factor in the effectiveness of a law, then public (and criminal) awareness is of particular importance. Awareness can mitigate a law’s potential effects, as when firearms are purchased at increased rates prior to the implementation of a ban.
- Duration of exposure and follow-up: Follow-up periods of less than 2 years may be inadequate to assess the long-term societal effects of a law. It will be useful to determine whether specific laws have immediate or gradual impact, and how effects change over time.
Measurement of Violent Outcomes
- Specific measures: Studies should measure outcomes directly associated with the law being evaluated (e.g., violence outside the home for laws about firearm carrying outside the home, and child violence perpetration for laws about child access to and use of firearms in the home). Failure to do so may result from a lack of information on direct measures of the outcome of interest.
- Intermediate outcomes: Even when outcomes of interest are directly assessed, it may be useful to have information on intermediate outcomes in order to understand the way in which the outcome of interest is achieved (e.g., decreasing violence by changing firearm storage or carrying behavior).
- Population-specific effects: The measurement of the effects of laws (e.g., acquisition restrictions) on violence perpetrated by criminals is important. It is also important to measure or estimate overall population effects of the same laws, for example, whether felony conviction restrictions for firearm purchase affect not only rates of violence among people with felony convictions, but also rates of violence in the general population.
- Substitution of weapons: If the goal of a firearms law is the reduction of harm, it is essential to determine whether, given that one weapon may become less available because of the law, that weapon is not readily replaced by another that causes the same (or more or less) harm.
- Substitution of place: Similarly, given that many firearms laws are local, it is important to determine whether enacting a law in one location displaces harm from that setting to another (e.g., affecting crime in neighboring jurisdictions that do not have such a law).
Measurement of Potential Confounders and Effect Modifiers
- Measuring and adjusting for confounders: In the analysis of firearms laws, important confounders (e.g., gang activity, drug-related issues, crime cycles, law enforcement practices) are often difficult to measure. Better measures should be developed and used.
- Effect modification: It is critical to assess the conditions under which laws may work, may work best, and may not work (e.g., alone or in combination with other laws, or in some settings but not in others). Many laws have multiple provisions, and it is important to determine which combinations of laws or provisions are most effective.
- Appropriate design and analytic techniques: Where possible, the data should be collected as prospective time-series measurements; analyses of trends are preferable to analyses of before-and-after changes. Analytic techniques should include appropriate adjustment for autocorrelation of data in time-series and in adjacent geographical locations.
- Assumptions and validation: Analytic techniques commonly rest on assumptions about the study design or the characteristics of the study data. Assumptions should be validated and, to the extent that they are violated, the consequences of violation considered and addressed.
The reviews also identified potential research questions related to outcomes in addition to violence. These include:
- Property crime
- Assess the effects of firearms laws on property crime.
- Assess the effects of firearms laws on people's capacity to defend themselves legally.
- Determine whether all demographic population segments are similarly affected.
- Legal rights
- Assess the effects of firearms laws on legal rights. For example, expulsion under the Gun-Free Schools Act to keep schools safe may conflict with the rights of students to an education.
- Assess the effects of firearms laws (such as licensing, registration, background checks of applicants) on the apprehension of "wanted persons," such as fugitives from justice.
- Assess the costs and benefits associated with implementing and enforcing firearms laws.
Vernick JS, Hepburn LM. State and federal gun laws: trends for 1970–1999. In: Cook PJ, Ludwig J, eds. Evaluating Gun Policy. Washington (DC): Brookings Institution Press, 2003:345–402.
Studies examined the effects of restrictions based on prior felony conviction (2 studies), misdemeanor convictions (1 study), or "mental defective" status, drug abuse, alcohol, and (unspecified) age restrictions (1 study).