Source: Jimmy Chan
Deterrence is a complex topic. A starting point for the discussion: National Institute of Justice: Five Things About Deterrence:
1) The certainty of being caught is a vastly more powerful deterrent than the punishment.
2) Sending an individual convicted of a crime to prison isn’t a very effective way to deter crime.
3) Police deter crime by increasing the perception that criminals will be caught and punished.
4) Increasing the severity of punishment does little to deter crime.
5) There is no proof that the death penalty deters criminals.
The article elaborates on each section. It does not break out gun crimes.
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Generally speaking, criminal policies that limit themselves to harsh(er) penal policies are unlikely to be effective in terms of either preventing crime from happening, or criminals from relapsing.
Taken together, studies on the relationship between punishment and deterrence point to the direction that increasing severity of punishment provides little gains, and if it has a noticeable effect, the relative costs can be high.
For example, among those who found severe punishment to have a noticeable effect, there is Helland and Tabarrok who studied California’s Three strikes law which appears to reduce felony arrest rates “among the class of criminals with two strikes by 17-20 percent”.
However, deterrence in the realm of 31,000 crimes a year is not without importance but the three strikes law also requires that considerable resources be spent on long-term, expensive imprisonment. Three strikes prisoners must serve at least a twenty year sentence before they are even eligible for parole and some will never be released […]
It costs approximately $0.58 million to imprison third strikers. So if there are 8000 third strikers imprisoned it would come to $4.6 billion ($0.58 million * 8000 prisoners) or $148,000 per crime avoided. This is a large figure given estimated costs per crime range around $34,000.
That said, several reviews and/or meta-analyses (see for example Paternoster, Durlauf and Nagin, Nagin and Chalfin and McCrary) have found that there is ultimately little evidence supporting severe punishment as an effective deterrent mean.
Paternoster (2010)
The empirical evidence leads to the conclusion that there is a marginal deterrent effect for legal sanctions, but this conclusion must be swallowed with a dose of caution and skepticism. It is very difficult to state with any precision how strong a deterrent effect the criminal justice system provides. At the very least, there is a great asymmetry between what is expected of the legal system through deterrence and what the system delivers.
There is greater confidence that non-legal factors are more effective in securing compliance than legal threats. It is argued that the empirical evidence does support the belief that criminal offenders are rational actors, in that they are responsive to the incentives and disincentives associated with their actions, but that the criminal justice system, because of its delayed imposition of punishment, is not well constructed to exploit this rationality.
Durlauf and Nagin (2011)
With respect to broad conclusions, we believe that it is reasonably clear that lengthy prison sentences particularly in the form mandatory minimum-type statutes such as California’s Three Strikes Law are difficult to justify on a deterrence-based, crime prevention basis. They might be justifiable based on either incapacitation benefits or along retributive lines.
If one takes the total resources devoted to crime prevention as fixed, then our conclusions about the marginal deterrent effects of certainty and severity suggest that crime prevention would be enhanced by shifting resources from imprisonment to policing […] Another possible candidate beneficiary beside the police for a crime-reducing resource shift would be enhanced probation and parole supervision services along the lines of Project Hope […]
Nagin (2013)
Studies of changes in police presence, whether achieved by changes in police numbers or in their strategic deployment, consistently find evidence of deterrent effects. Studies of the deterrent effect of increases in already long prison sentences find at most a modest deterrent effect. Studies of the deterrent effect of capital punishment provide no useful information on the topic.
Chalfin and McCrary (2017)
Evidence in favor of deterrence effects is mixed. While there is considerable evidence that crime is responsive to police and to the existence of attractive legitimate labor-market opportunities, there is far less evidence that crime responds to the severity of criminal sanctions.
Therefore, the NIJ page shared by the other user provides a good enough summary of what is understood about deterrence.
What about guns specifically? According to Chalfin and McCrary whilst examining the earliest literature (Loftin and McDowall 1981; Loftin, Heumann, and McDowall 1983; Loftin and McDowall 1984; and McDowall, Loftin, 31A 2009 review of the literature by Donohue reaches a similar conclusion. and Wiersma 1992) considered the effects of sentence enhancements for specific crimes—particularly gun crimes—generally finding little evidence in favor of deterrence.
Raphael and Ludwig assessed of Richmond’s Project Exile, a sentence enhancement program which “increased the prison penalties for carrying guns by those with prior felony convictions”. They compared adult homicide arrest rates and juvenile homicide arrest rates (“[t]ypically only adults are eligible for the “felon-in-possession” prosecutions”) and compared Richmond with other cities. The results presented now and in the previous section taken together do not provide support for the idea that Project Exile had any detectable effect on homicide rates in Richmond or in the larger set of cities that began to divert eligible gun offenders from state to federal courts.
I will note that Rosenfeld et al. argue that there was, in fact, an intervention effect of Project Exile after analyzing a longer time series, but: The Richmond results inspire somewhat greater confidence in the existence of a difference between Richmond’s firearm homicide trend and the average trend for the sample, although the difference may have been quite small […]
In summary, we find evidence consistent with an intervention effect on homicide trends for Richmond’s Project Exile. Richmond’s firearm homicide rate fell more rapidly than the average firearm homicide rate among large U.S. cities, with other influences controlled. We cannot rule out the possibility that unmeasured factors are responsible for Richmond’s drop in firearm homicides after Exile was introduced in 1997. However, they apparently do not include changes over time in police size, drug involvement, or incarceration rates, all prime candidates for explaining the decline in big-city homicide rates during the 1990s (Rosenfeld, 2004).
It is worth noting since then that international studies about the crime drop referred to by Rosenfeld et al. have shown that incarceration rates are unlikely to explain the phenomenon. See for example Farrell et al.‘s review:
Overall, there is little evidence that imprisonment played much, if any, role in the crime drop even in the United States and no evidence that it played a role in most other countries experiencing a crime drop.
If the goal is to deter gun crime, research would suggest the pursuit of criminal policies which do more than increasing the severity of punishment. It should act, for example, on opportunity, increasing certainty of punishment and promoting effective policing models and strategies (and for offenders, evidence-based rehabilitation programs).
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