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We have documented what is known about how people obtain firearms

for criminal activities and identified the weaknesses of existing evaluations

of interventions. There is not much empirical evidence that assesses whether

attempts to reduce criminal access to firearms will reduce gun availability

or gun crime. Most research has focused on determining whether prohibited

persons illegally obtain firearms from legitimate commerce (legal primary

and secondary markets) or whether crime guns are stolen or acquired

through informal exchanges. Current research evidence suggests that illegal

diversions from legitimate commerce are important sources of guns and

therefore tightening regulations of such markets may be promising. There

also may be promising avenues to control gun theft and informal transfers

(through problem-oriented policing, requiring guns to be locked up, etc.).

We do not yet know whether it is possible to actually shut down illegal

pipelines of guns to criminals or what the costs of such a shutdown would

be to legitimate buyers. Answering these questions is essential.

We also provide an analytic framework for assessing interventions.

Since our ultimate interest is in the injuries caused using guns and not how

guns are obtained, the key question involves substitution. In the absence of

the pathways currently used for gun acquisition, could individuals have

obtained alternative weapons with which to wreak equivalent harm?

Substitution has many dimensions; time, place, and quality are just

some of them. For example, that crime guns tend to be newer than guns

generally indicates that criminals prefer new guns, even though old guns are

generally as easy to get and are cheaper. This may be strictly consumer

preference, or it may be to avoid being implicated, through ballistics imaging,

in other crimes in which the gun was used. Would offenders currently

using newer guns use older guns—or any guns—if access to newer guns

became more limited? If particular dealers account for a disproportionate

share of crime weapons, then we are left with yet another version of the

substitution question: Would the criminals have obtained other guns, with

similar harmful effects, from other sources, including other FFLs? How

long would this process of substituting from new to old or from one source

to another take?

What data are needed to determine the extent of substitution among

firearms? Much could be learned from individual-level data from a general

population survey on the number of guns owned by length of time, along

with detailed individual characteristics of the individual (age, demographic

characteristics, psychiatric history, other high-risk behaviors), along with

type of gun owned (if any) and the method of acquisition (retail purchase,

legal purchase of used gun, illegal purchase of stolen gun, borrowed through

informal network). In addition, one would want measures of the availabil100

ity of firearms of each type to potential buyers of each type in each locale.

For adults without criminal records, for example, there are established,

observable prices of new guns at retail outlets. Similarly, there are active

markets in used guns, for which there are (at least in principle) prices. The

prices are individual specific in the sense that, for example, juveniles and

felons cannot purchase guns at Wal-Mart.8 In effect, they face an infinite

price of guns through this channel.

Beyond this information one would also need a source of exogenous

variation on the difficulty of obtaining guns through different channels.

While guns available to legal buyers through retail outlets have literal prices,

the measures of the difficulty of gun acquisition through some other channels

are prices only in a metaphorical sense. When a city undertakes an

intervention at a particular point in time, for example to make it more

difficult for juveniles to get guns from interstate traffickers in new guns,

then (provided that the policy has some effect), it is as if the price of guns to

juveniles has risen. Provided that the timing of the intervention is independent

of the time pattern of local gun use, we could treat it as an exogenous

increase in the metaphorical price of a gun to juveniles; money prices may

fall as other costs rise because this increase in nonmoney costs shifts the

demand curve down. What happens to the tendencies for juveniles to obtain

guns; do they substitute purchases of guns stolen from homes for the

new guns they had previously purchased from traffickers? Is the substitution

complete? That is, is the volume of juvenile gun use as high in the

presence of the intervention as it was in the absence of the intervention?

The biggest potential problem with this framework, however, is the

assumption of an exogenous intervention. No real intervention is likely to

be exogenous; that is, unrelated to changes in gun crimes. It might be more

realistic to think about exogeneity conditional on some specified set of

covariates, but the prospects for finding consensus on the correct set of

covariates to credibly maintain this independence assumption are unknown.

Alternatively, researchers may be forced to rely on other methodological

approaches and data.

The committee has not attempted to identify specific interventions,

research strategies, or data that might be suited for studying market interventions,

substitution, and firearms violence. The existing evidence is of

limited value in assessing whether any specific market-focused firearm restrictions

would curb harm. Thus, the committee recommends that work be

started to think carefully about the prospects for achieving “conditional

exogeneity,” the kinds of interventions and covariates that are likely to

8We ignore for the moment corrupt agents at retail outlets, viewing them as the equivalent

of straw purchasers.

satisfy this independence requirement, how one could gather the data, the

potential for building in evaluation at the stage of policy change, and other

possible research and data designs. Future work might begin by considering

the utility of emerging data systems, described in this report, for studying

the impact of different market interventions, This type of effort should be

take place in collaboration with a group of survey statisticians, social scientists,

and representatives from the Bureau of Justice Statistics and the National

Institute of Justice.