A policy of mass incarceration in the U.S., beginning in the late 1970s and early 1980s, caused huge increases in the number of people in prisons and jails. Both the likelihood of incarceration and average sentence length increased substantially (Mauer 2006; Western 2006). While there were two million adults in the correctional system in 1980 (on probation or parole or in prisons and jails), the number ballooned to 6.5 million in 2000 and has remained fairly stable since then (Glaze and Herberman 2014; Mears, Cochran, and Cullen 2015). There were about seven million adults in the correctional system in 2014ā4.7 million on probation or parole and 2.2 million in prisons or jails. One out of 36 adults (or about 3 percent of all adults) at the time was under some form of correctional supervision (Kaeble, Glaze, Tsoutis, and Minton 2015). The picture is worse for some populations, such as African Americans. Among men born in the late 1960s, ā3 percent of whites and 20 percent of blacks had served time in prison by their early thirtiesā (Petit and Western 2004: 151).
Legal punishment, such as imprisonment, has diverse goals, including retribution, rehabilitation, incapacitation, and deterrence. Except for retribution which has ancient roots, deterrence is the oldest of the goals, with its foundations in the writings of eighteenth-century Enlightenment philosophers, such as Cesare Beccaria and Jeremy Bentham (Johnson and Wolfe 2003). Deterrence is also the most complex, which is one reason why, many years after Beccaria and Bentham, researchers still know very little about it. Part of the complexity is that the concept of deterrence is multidimensional; there are different types of deterrence, and the effects may vary from one type to the next. The causal logic of deterrence is also complex, and there are challenges in distinguishing deterrent effects from other effects of legal punishment, such as incapacitation.
This chapter focuses on the deterrent effects of imprisonment. Along with incapacitation, deterrence has been one of the principal justifications for mass incarceration in the U.S. (Mears and Cochran 2015; Mears et al. 2015). Increased imprisonment should incapacitate more people from committing crimes (i.e., prevent them from committing crimes while in prison) and/or deter more people from committing crimes because of fear of being imprisoned or re-imprisoned. The chapter also considers what constitutes relevant evidence of the deterrent effects of imprisonment and the quality of the evidence in existing research. A good place to begin is examination of crime trends.
In the U.S. from the early 1960s to the early 1980s, there were increases in both property and violent crime rates (Paternoster 2010). The increases were followed by decreases in both rates until the mid 1980s when they increased again. Both rates peaked in the early 1990s; but after that, there were substantial decreases that have been labeled āthe great American crime declineā or simply āthe crime dropā (Blumstein and Wallman 2000; Zimring 2006). The drop occurred at the time when mass incarceration in the U.S. was causing the imprisonment rate to double, raising the question whether increased imprisonment was responsible (Paternoster 2010). As Paternoster (2010: 801) indicated, āthere is a general consensus that the decline in crime [was], at least in part, due to more and longer prison sentences,ā but there is disagreement about āhow much of an effect imprisonment hadā (also see Rosenfeld and Messner 2009). Spelman (2000) estimated that between 4 percent and 21 percent of the drop was due to increased imprisonment, while Levitt (2004) estimated it to be 33 percent. Whatever the magnitude of the effect, it has been difficult to estimate how much of it was due to deterrence and how much to incapacitation. It was probably both. Moreover, researchers have found the crime drop to be better explained by factors other than imprisonment, such as decreasing demand for crack and other hard drugs, an expanding national economy and increasing consumer confidence, changes in crime reporting, an aging population, and improvements in domestic security (e.g., Blumstein and Wallman 2000; Farrell, Tseloni, Mailley and Tilley 2011; Rosenfeld and Messner 2009; Steffensmeier and Harer 1999).
One of the goals of this chapter is to explain why caution is needed in considering all evidence about the deterrent effects of imprisonment. The evidence is mixed, with some studies suggesting that imprisonment deters, while other studies suggesting it does not. More importantly, many of the studies have serious shortcomings that limit their usefulness in assessing the deterrent effects of imprisonment and constructing effective crime-control policy.
Background
Briefly defined, deterrence is the omission or curtailment of crime out of fear of legal punishment, including imprisonment (Gibbs 1975). The terms omission and curtailment in the definition are important because they suggest two possibilities. People may refrain entirely from committing a crime out of fear of legal punishment, which is termed absolute deterrence. Or they may only curtail or restrict their crimes out of fear of legal punishment as when a burglar takes a temporary break, believing that additional burglaries will result in a substantial increase in the likelihood of being caught. This second possibility is termed restrictive deterrence.
Three properties of legal punishment are relevant for deterrence: certainty, severity, and celerity. Any type of legal punishment (e.g., community service, restitution, or probation) can be considered in terms of these properties, but for imprisonment, certainty has to do with the probability of being imprisoned for crime. Severity has to do with the amount of punishment from imprisonment, including sentence length. Celerity has to do with the speed or swiftness at which people are imprisoned after committing a crime (or, alternatively, the speed at which they are sentenced to prison).
Since Beccaria and Benthamās writings, the certainty of legal punishment has been considered a more effective deterrent than either severity or celerity and, consequently, has been the focus of most deterrence research (Paternoster 2010). Moreover, while traditional accounts of deterrence consider speedier punishments to be greater deterrents, some people may perceive delayed punishment as more severe because it gives them time to dread what is ahead for them. If so, speedy punishment should be less of a deterrent. Because the possibility of dread creates ambiguity about how the celerity of punishment works as a deterrent (if at all), there has been little research on it (for exceptions, see Clark 1988; Nagin and Pogarsky 2001). Consequently, the focus here is on the certainty and severity of imprisonment.
There are two ways to consider certainty and severity. The first is to consider them objectively. Objective legal punishments involve what legal officials actually do in the way of punishing offenders. For example, for a particular place and time, such as a U.S. state in a given year, the objective certainty of imprisonment for a type of crime could be estimated by dividing the number of persons imprisoned for the crime divided by the number of crimes. There are two predictions about the objective certainty and severity of imprisonment and the likelihood of crime:
1. The greater the objective certainty of imprisonment for a type of crime, the less the likelihood of the crime.
2. The greater the objective severity of imprisonment for a type of crime, the less the likelihood of the crime.
The second way to consider legal punishments is perceptually. People can be asked about their perceptions of the certainty and severity of imprisonment in a survey or in interviews. The distinction between objective and perceived punishments is important because, according to the causal logic of deterrence, objective punishments deter only indirectly through their effects on perceived punishments (Gibbs 1975). Peopleās perceived punishments are believed to result from objective punishments (what legal officials actually do), and deterrence is believed to occur when people perceive legal punishments as certain and severe. There are two predictions about the perceived certainty and severity of imprisonment and the likelihood of crime:
1. The greater the perceived certainty of imprisonment for a type of crime, the less the likelihood of the crime.
2. The greater the perceived severity of imprisonment for a type of crime, the less the likelihood of the crime.
A complication is that there are two types of deterrence: specific and general (Gibbs 1975; Stafford and Warr 1993). Whereas specific deterrence has to do with the deterrent effects of peopleās direct experience with legal punishment (including avoidance of punishment), general deterrence has to do with the deterrent effects of peopleās indirect experience with legal punishment through observing or somehow learning about the punishment experiences of others (also including avoidance of punishment). To illustrate, if a judge sentences a burglar to prison to send him a message to refrain from burglary after release, the judgeās goal is specific deterrence. If the judge sentences the burglar to prison to send a message to others to refrain from burglary, the judgeās goal is general deterrence. While probably all judges sentence burglars to prison to achieve both types of deterrence, imprisonment may deter only specifically and not generally, or only generally and not specifically. The point is there is no reason to expect that imprisonment, or any type of legal punishment, will necessarily result in both specific and general deterrence.
Research on General Deterrence and Imprisonment
Despite its eighteenth-century foundations, discussions of deterrence were largely argumentative and ideological until the late 1960s when Gibbs (1968) and Tittle (1969) first tested two key deterrence predictions. Gibbs (1968) examined the relationship among U.S. states between the objective certainty and severity of imprisonment and the homicide rate (Predictions 1 and 2 above). Objective certainty was estimated for each state by dividing the number of persons admitted to prison for homicide during 1959ā1960 by the average annual number of homicides during the same period. The objective severity of imprisonment for each state was estimated by the median number of months served in prison for homicide as of December, 1960. Consistent with Prediction 1 above, states with greater objective certainty of imprisonment had lower homicide rates. Consistent with Prediction 2 above, states with greater objective severity of imprisonment also had lower homicide rates, but the association was small and not statistically significant.
Tittle (1969) expanded on Gibbsā (1968) study by examining 1960s state-level imprisonment data for more types of crimeārape, robbery, assault, burglary, theft, and auto theft in addition to homicide. Across all crime types, states with greater objective certainty of imprisonment had lower crime rates. The magnitude of the association, however, varied from a large association in the case of rape to no association in the case of auto theft (Tittle 1969). Moreover, contrary to Prediction 2 above, states with greater objective severity of imprisonment had higher crime rates. Homicide was the only exception. Consistent with Prediction 2 above, the greater the objective severity of imprisonment for homicide in a state, the less the stateās homicide rate. The objective certainty of imprisonment was, on average, greater for homicide than for other types of crime, which led to Tittle (1969) suggesting that greater objective severity may deter only when objective certainty is high. āIt would seem that severity alone is simply irrelevant to the control of crimeā (Tittle 1969: 416).
Alternative Interpretations
The importance of Gibbsā (1968) and Tittleās (1969) groundbreaking studies should not be underestimated, but the findings were subject to alternative interpretations. Gibbs (1968) observed that social condemnation of homicide could produce a lower homicide rate, and it also could produce greater objective certainty and severity of imprisonment for homicide. The observed association between the objective certainty/severity of imprisonment and the homicide rate could, therefore, be spurious. Erickson, Gibbs, and Jensen (1977: 316ā317) later elaborated:
A criminal law is seldom violated if the type of act is socially condemned to a marked degree, and that very condemnation prompts legal officials to pursue arrests and press for convictions. Those official activities could result in greater objective certainty of punishment than would otherwise be the case ā¦, and the greater objective certainty may be perceived by the public ⦠in terms of āwhat ought to beā ⦠The combination of a low crime rate ⦠and high objective or perceived certainty of legal punishment would reflect the social (extralegal) evaluations of particular types of crimes, not deterrence. That possibility is ⦠important since there is no basis to assume that the social condemnation of particular types of crime (e.g., homicide) is even approximately constant from one state to the next.
Tittle (1969) likewise considered an alternative interpretation of his findings. Because his data were cross-sectionalāthe imprisonment and homicide data covered roughly the same period in the early 1960sāit was impossible to distinguish cause from effect. A low crime rate could have caused greater objective certainty of imprisonment rather than the other way around. āThis may come about because fewer crimes permit police departments to assign more manpower to known crimesā (Tittle 1969: 420). Conversely, a high crime rate could have led to a low objective certainty of imprisonment. āHigh crime rates could result in overcrowded prison facilities, thus inducing judicial personnel to make greater use of probation and suspended sentencesā (Tittle 1969: 420).
There is still another alternative interpretation of the GibbsāTittle findings. Imprisonment can eliminate opportunities to commit crime. It is difficult, if not impossible, to commit some types of crime, such as auto theft, in prison. Thus, imprisonment can incapacitate offenders from committing crimes. In such a case, āthe greater the [objective] certainty [and severity] of imprisonment, the greater the incapacitation, and the less the crime rateā (Gibbs 1975: 60). The same association between the objective certainty and severity of imprisonment and the crime rate could reflect deterrence or incapacitation, or both.
Deterrence versus Incapacitation
Why is it important to distinguish the effects of deterrence from incapacitation? If imprisonment produces less crime, why ask the reason? Gibbs (1975: 59) answered this way:
Consider two jurisdictions, A and B, with approximately the same population size. Suppose that in A during a particular year there were 100 cases of robbery, with 20 individuals accounting for 40 cases before being imprisoned. Now suppose that another 20 individuals committed robbery at least once without ever being imprisoned so that they accounted for the remaining 60 cases, or 3 per individual. Turning to jurisdiction B suppose that there were also 40 individuals who committed robbery at least once during a year, but that only 5 were imprisoned, having committed 10 robberies prior to arrest. So the remaining 35 committed 105 robberies (3 on the average) without being imprisoned ⦠Bās robbery rate (115 cases) would be greater than Aās (the two having the same population size), and the [objective] certainty of imprisonment would be greater in A. Those differences would be consistent with the deterrence doctrine, but the contrasts in the robbery rates could be attributed entirely to incapacitation. Had 15 more B individuals been imprisoned before repeating the offense, the robbery rates of A and B would have been equal, and the [objective] certainty of imprisonment would have been equal.
It is important to emphasize that if imprisonment only incapacitates without deterring, it can only prevent crimes that offenders would commit if they were not in prison (in the Gibbs example above, 40 robberies in jurisdiction A and ten robberies in jurisdiction B). More crimes could be prevented if imprisonment deterred people outside of prison from committing crimes (general deterrence). Deterrence would have broader applicati...