When planning a cluster randomized trial, evaluators often have access to an enumerated cohort representing the target population of clusters. Practicalities of conducting the trial, such as the need to oversample clusters with certain characteristics in order to improve trial economy or support inferences about subgroups of clusters, may preclude…

Discusses ethical issues surrounding passive and active parental consent procedures when minors are to be asked sensitive research questions, exploring parental rights and the effect of active consent procedures on response rates and sample bias. Response rates are reported from two studies in which active consent procedures were implemented. (SLD)

Prediction of success in a special program often guides program participant selection and treatment. If the statistical analysis used to develop such predictions is based on the special selectivity built into the program, the predictions can be misleading and the validation tests uninformative. Federal district court pretrial release data is used…

Differences between means, variance, and correlation parameter estimates from a full school sample and samples restricted by parental consent were studied with 1,609 students at continuation high schools and 1,192 at traditional high schools. Sample bias due to consent policies may not be a substantive problem, especially if a telephone consent…

Tracking and two statistical methods (probability weighting and sample selection modeling) were studied as ways to minimize bias attributable to sample attrition in school-based studies. Data on student smoking from 30 middle schools illustrate that sample weighting yields the best results, with estimates superior to sample selection and much less…

A beverage-server intervention project at two West Coast Navy bases that attempted to reduce levels of alcoholic intoxication via policy changes and server training is described. Data obtained via interviews and structured observations of 1,511 club customers indicate methodological bias and self-selection effects. Bias adjustments were performed…