Confusion about the meaning of validity in quasi-experimental research can be addressed by carefully relabeling types of validity. Internal validity can more aptly be termed "local molar causal validity." More tentatively, the "principle of proximal similarity" can be substituted for the concept of external validity. (Author)

Modeling the process by which participants are selected into groups, rather than adjusting for preexisting group differences, provides the basis for several new approaches to the analysis of data from nonrandomized studies. Econometric approaches, the propensity scores approach, and the relative assignment variable approach to the modeling of…

Causal models often omit variables that should be included, use variables that are measured fallibly, and ignore time lags. Such practices can lead to severely biased estimates of effects. The discussion explains these biases and shows how to take them into account. (Author)

Twenty-nine steps necessary for data file preparation for secondary analysis are discussed. Data base characteristics and planned use vary the complexity of the preparation. Required techniques (file verification, sample verification, file merger, data aggregation, file modification, and variable controls) and seven associated pitfalls are defined…

Time series analysis is applied to an assessment of the temporary and permanent impact of the 1975 Australian Family Law Act and its effect on number of divorces. The application and construct validity of the model is examined. (Author/PN)

The 9 articles of this theme issue stem from a project on alcohol and drug abuse that involved 14 projects, 10 of which began with randomized clinical trials. These papers describe implementation problems associated with experimentation in field research and the focus on ensuring internal validity. (SLD)