This Campbell systematic review compares effects of custodial and non‐custodial sentences on re‐offending. The authors found 14 high‐quality studies, including three randomised controlled trials and two natural experiments. Imprisonment is no more effective than community‐based sanctions in reducing re‐offending. Despite this evidence, almost all societies across the world continue to use custodial sentences as the main crime control strategy. In terms of rehabilitation, short confinement is not better or worse than “alternative” solutions. 1 Synopsis As part of a broad initiative of systematic reviews of experimental or quasi‐experimental evaluations of interventions in the field of crime prevention and the treatment of offenders, our work consisted in searching through all available databases for evidence concerning the effects of custodial and non‐custodial sanctions on re‐offending. For this purpose, we examined, in 2006, more than 3,000 abstracts, and identified more than 300 possibly eligible studies. For the update, nearly 100 additional potentially eligible studies published or completed between 2003 and 2013 have been identified. For the update, 10 matched‐pair design studies and one RCT have been abstracted. One study (Bergman 1976) that, in 2006, had been classified as an RCT turned out, after closer examination, to have been quasi‐experimental with respect to the comparison of the custodial and the non‐custodial groups. As a result, it has been “downgraded” and included among the quasi‐experimental studies in this update. The findings of the update confirm one of the major results of the first report, namely that the rate of re‐offending after a non‐custodial sanction is lower than after a custodial sanction in most comparisons. However, this is true mostly for quasi‐experimental studies using weaker designs, whereas experimental evaluations and natural experiments yield results that are less favourable to non‐custodial sanctions. It can be concluded that results in favour of non‐custodial sanctions in the majority of quasi‐experimental studies may reflect insufficient control of pre‐intervention differences between prisoners and those serving “alternative” sanctions. 2 Abstract BACKGROUND Throughout the Western World, community‐based sanctions have become a popular and widely used alternative to custodial sentences. There have been many comparisons of rates of reconviction among former prisoners and those who have served any kind of community sanction. So far, the comparative effects on re‐offending of custodial and non‐custodial sanctions are largely unknown, due to many uncontrolled variables. OBJECTIVE The objective is to assess the relative effects of custodial sanctions (imprisonment) and non‐custodial (“alternative” or “community”) sanctions on re‐offending. By “custodial” we understand any sanction where offenders are deprived of freedom of movement, i.e. placed in a closed residential setting not their home, no matter whether they are allowed to leave these premises during the day or over weekends. Thus, jails and boot camps would be considered “custodial” settings according to the definition adopted here. By “non‐custodial”, we mean any form of sanction that does not involve any deprivation of liberty, such as community work, electronic monitoring, financial or suspended custodial sanctions. Thus, the category of non‐custodial sanctions includes a great variety of punishments that have in common leaving the offender in the community rather than putting him into confinement. SEARCH STRATEGY Relevant published and unpublished studies which meet the eligibility criteria have been identified, during the first as well as for the updated review, through multiple sources, including Abstracts, bibliographies, and contacts with experts in several countries. In particular, the following sources have been searched for abstracts: Criminal Justice Abstracts, Criminology and Penology Abstracts, National Criminal Justice Reference Service (NCJRS), Library Catalogues (University of Minnesota), http://www.google.ch. The following keywords have been used to identify relevant studies: Prison, jail, imprisonment, alternative sanctions, house arrest, electronic monitoring, community service, probation, day reporting, fines, shock incarceration, boot camps; further keywords: re‐conviction, re‐offending, self‐reported offenses, recidivism, re‐arrest and re‐incarceration. ELIGIBILITY CRITERIA Randomized or natural experiments, as well as quasi‐experimental comparisons between former prison inmates and those who served community sanctions have been included without exception, provided that propensity score matching methods were used. Other quasi‐experimental studies have been included, for the updated as well as the first review, if subject were matched or if three or more potentially relevant independent variables had been controlled for. Studies written in any language and prepared between 1961 and 2013 have been considered for inclusion. For the update, ten studies have been identified and considered that used propensity scores in order to control for pre‐existing differences between custodial and non‐custodial groups. DATA COLLECTION AND ANALYSIS A coding protocol has been prepared, following the guidelines of the Campbell Collaboration. MAIN RESULTS Although a majority of the selected studies (see Table 2) show non‐custodial sanctions to be more beneficial in terms of re‐offending than custodial sanctions, no significant difference is found in the meta‐analysis based on four controlled and one natural experiments. It should be noted that offences prevented through incapacitation of incarcerated offenders have not been considered in this assessment. REVIEWERS' CONCLUSIONS The review has allowed identifying several shortcomings of studies on this subject: 1) Controlled experiments are still rare exceptions, although obstacles to randomisation are often less formidable than claimed. 2) Follow‐up periods rarely extend beyond two years. Even in cases of controlled trials where later follow‐up studies might be feasible, periods considered rarely extended to significant parts of subjects' biographies. 3) Despite alternative (and presumably more valid) measures of re‐offending (such as self‐reports) have become widely available, most studies do not include measures of re‐offending beyond re‐arrest or re‐conviction. 4) In most studies, only the occurrence (prevalence) of re‐arrest or reconviction is considered, but not the frequency (incidence) of new offences. Some studies have shown, however, that most offenders reduce offending rates after any type of intervention. Thus, the relevant question may be to what extent improvement differs by type of sanction. Therefore, future studies should look at rates of improvement (or reductions in offending) rather than merely at “recidivism” as such. 5) Rehabilitation in other relevant areas, such as health, employment, family and social networks, is rarely considered, despite century‐old claims that short custodial sentences are damaging with respect to social integration in these other areas. 6) No study has addressed the possibility of placebo (or Hawthorn) effects. Even in controlled trials, it is not clear to what extent outcomes that favoured “alternative” sanctions were due to the fact that subjects assigned to non‐custodial sanctions may have felt treated more fairly, rather than to specific effects of “alternative” sanctions as such. Given experimental research on neurobiological effects of feelings of fairness (Fehr and Rockenbach, 2003), such a possibility should be envisaged with more attention in future research. SOURCES OF SUPPORT The update has been supported by a grant of the Swedish National Council for Crime Prevention. The original review, published in 2006, was supported by a grant of the Swiss National Science foundation.