SELECTIVE INCAPACITATION,THREE STRIKES,AND THE PROBLEM OF AGING PRISON POPULATIONS: USING SIMULATION MODELING TO SEE THE FUTURE*

Research Summary: The growth of prison populations over the last three decades is a great source of concern for policy makers and observers. One mechanism by which this growth occurs is via sentencing reforms that extend length of stay for certain categories of offenders. This has the effect of aging prison populations, which is problematic for many reasons. Apart from the increased financial burdens entailed in caring for older prisoners, it is also important to consider the intent of reforms in evaluating them. Of late, sentencing reform has become increasingly focused on the selective incapacitation of dangerous offenders. Policies that have the effect of aging the prison population are problematic from this perspective due to the diminishing returns realized with respect to incapacitation as offenders age. Dynamic systems simulation analysis is employed to investigate the likely consequences of recent sentencing reforms that increase length of stay for some offenders. These analyses indicate that the effects of recent reforms may not be as dramatic as some observers have predicted, but they suggest that the consideration of alternatives to incarceration for elderly offenders is warranted from the standpoint of cost considerations as well as that of selective incapacitation. Policy Implications: The results indicate that California's Three Strikes law will not accelerate the rate of growth of the elderly prison population. However, even without increasing the proportional representation of elderly prisoners, the number of elderly prisoners is expected to grow substantially over the next three decades. These prisoners will strain criminal justice system resources while presenting little public safety threat. State criminal justice policy makers and their constituents should closely examine laws that impose very long stays without discretionary release, as these statutes may contribute to the production of elderly prisoners. This problem is particularly pronounced in Three Strikes and other habitual offender laws that use retrospective methods to identify habitual offenders. Additionally, the effects of reforms lengthening stay for some offenders must be considered in light of cumulative effects of sentencing reform resulting in changes to the demographic structure of the prison population overall. Dynamic systems simulation modeling is presented as a valuable policy‐making tool, as it allows the policy analyst to examine the potential impacts of laws in the absence of data suitable for conventional statistical analyses.     

The Silence of the Lambdas: Deterring Incapacitation Research

This essay provides an economist’s perspective on criminological research into incapacitation effects on crime. Our central argument is that criminologists would do well to substantially scale back the enterprise of trying to estimate the various behavioral parameters central to a micro-level approach to measuring incapacitation effects, including the annual rate of offending outside of prison (λ) and the lengths of criminal careers. One problem with this line of research is practical: for example, mean estimates of self-reported criminal activity by incarcerated prisoners are quite sensitive to reports by the most criminally active offenders. But the larger concern is conceptual—the incapacitation effects from a given change in sentencing policy may be undermined by the possibility of replacement effects, and at the same time omit other benefits that may arise from deterrent effects on crime. A more promising approach is to identify plausibly exogenous changes in sentencing policy in order to estimate the net impact on crime from the combined effects of incapacitation, deterrence and replacement.

Estimating the Number of Crimes Averted by Incapacitation: An Information Theoretic Approach

This paper presents an information theoretic approach for estimating the number of crimes averted by incapacitation. It first develops models of the criminal history accumulation process of a sample of prison releasees using their official recorded arrest histories prior to incarceration. The models yield individual offending trajectories that are then used to compute the number of crimes these releasees could reasonably have been expected to commit had they not been incarcerated—the counterfactual of interest. The models also afford the opportunity to conduct a limited set of policy simulations. The data reveal a fair amount of variation among individuals both in terms of the number of crimes averted by their incarceration and the responsiveness of these estimates to longer incarceration terms. Estimates were found not to vary substantially across demographic groups defined by offender race, gender, or ethnicity; variations across states and offense types were more pronounced. Implications of the findings and promising avenues for future research are discussed.

Incapacitation: Revisiting an Old Question with a New Method and New Data

We use the National Longitudinal Survey of Youth 1997 to obtain estimates of the number of crimes avoided through incapacitation of individual offenders. Incarcerated individuals are matched to comparable non-incarcerated counterparts using propensity score matching. Propensity scores for incarceration are calculated using a wide variety of time-stable and time-varying confounding variables. We separately analyze juvenile (age 16 or 17) and adult (age 18 or 19) incapacitation effects. Our best estimate is that between 6.2 and 14.1 offenses are prevented per year of juvenile incarceration, and 4.9 to 8.4 offenses are prevented per year of adult incarceration.

Does Incapacitation Reduce Crime?

Questions and answers about incapacitation abound in all discussions about criminal justice policy. They are among the most pressing of all research issues, yet estimates about the incapacitation effect on crime vary considerably, and most are based on very old and incomplete estimates of the longitudinal pattern of criminal careers. This paper provides an overview of the incapacitation issue, highlights information on recent estimates of criminal careers that are useful to the incapacitation model, and outlines an ambitious research agenda for continued and expanded work on incapacitation and crime that centers on developing better estimates of the characteristics of criminal careers and their relevance to policy choices.

Revisiting Incapacitation: Can We Generate New Estimates?

A substantial body of empirical research examines how the huge expansion in incarceration in the United States since the early 1970s has influenced crime. These studies merge the effects of three conceptually distinct paths by which incarceration might reduce crime: general deterrence, specific deterrence and incapacitation. This issue of the Journal focuses specifically on the incapacitation path. This Introduction reviews the individual papers and offers the editors’ judgment as to the plausibility of progress using different research strategies. It emphasizes the potential for using individual level data to take advantage of natural experiments.