Covariate adjustment can increase the precision of estimates by removing unexplained variance from the error in randomized experiments, although chance covariate imbalance tends to counteract the improvement in precision. The author develops an easy measure to examine chance covariate imbalance in randomization by standardizing the average…

In experimental designs with nested structures, entire groups (such as schools) are often assigned to treatment conditions. Key aspects of the design in these cluster-randomized experiments involve knowledge of the intraclass correlation structure, the effect size, and the sample sizes necessary to achieve adequate power to detect the treatment…

Evaluations that combine social science and law have tremendous potential to illuminate the effects of governmental policies and yield insights into how effectively policy makers' efforts achieve their aims. This potential is infrequently achieved, however, because such interdisciplinary research contains often overlooked substantive and…

Communities That Care (CTC) is a prevention system designed to reduce adolescent substance use and delinquency through the selection of effective preventive interventions tailored to a community's specific profile of risk and protection. A community-randomized trial of CTC, the Community Youth Development Study, is currently being conducted in 24…

Discusses advantages of randomized experiments and key issues raised in this special issue. Focuses on growth and decrease in the use of randomized experiments by the California Youth Authority, the U.S. National Institute of Justice, and the British Home Office. Calls for increased recognition of the importance of randomized experiments. (SLD)

Describes the randomized field trials conducted by the California Youth Authority in the 1960s and 1970s and discusses why such rigorous tests were used and why they eventually came to be used less often. (SLD)

Discusses the contrast between the frequency of randomized clinical trials in the health sciences and the relative famine of such studies in criminology. Attributes this difference to the contexts in which research is done and the difference in the status of situational research in the two disciplines. (SLD)

Introduces an new approach for measuring the impact of whole school reforms. The approach, based on "short" interrupted time-series analysis, is explained, its statistical procedures are outlined, and how it was used in the evaluation of a major whole-school reform, Accelerated Schools is described (H. Bloom and others, 2001). (SLD)

This article discusses the use of propensity scoring in experimental program evaluations to estimate impacts for subgroups defined by program features and participants' program experiences. The authors discuss estimation issues and provide specification tests. They also discuss the use of an overlooked data collection design--obtaining predictions…

Although some argue that randomization of treatments or interventions violates accepted norms of conduct of social science research, this article makes the case that there is a moral imperative for the conduct of randomized experiments in crime and justice studies. (SLD)

Describes and compares useful and unified power formulas for analysis of covariance and change-score analyses, indicating the implications of each for sample size requirements. Contains practical recommendations for evaluations and outlines a simple spreadsheet approach. (SLD)

Describes the history of the random experiment in the Home Office in the United Kingdom and demonstrates that research and the conduct of research is not an altogether rational process and that fashion, personality, and politics play a role in research policy and methodology choice. (SLD)

Describes the conceptual design, research framework, evaluation components, and analytic strategies that are guiding the evaluation of a demonstration-research effort, the American Stop Smoking Intervention Study (ASSIST). The ASSIST evaluation is a unique analysis of the relationships among social context, public-health activity, tobacco use, and…

Criteria for suitable research designs for use with large databases are suggested and analyzed. The advantages and disadvantages of several types of quasi-experimental designs are compared. Examples are taken from the authors' research with data from the Manitoba Health Services Commission. (Author/AL)

Effective early childhood intervention and child care policies should be based on an understanding of the effects of child care quality and type on child well-being. This article describes methods for securing unbiased estimates of these effects from nonexperimental data. It focuses on longitudinal studies like the one developed by the National…