Group design research studies can provide evidence to draw conclusions about "what works," "for whom," and "under what conditions" in special education. The quality indicators introduced by Gersten and colleagues (2005) have contributed to increased rigor in group design research, which has provided substantial…

An aspect of a study is considered a confounding factor if it is not possible to tell whether the difference in outcomes is due to the intervention, the confounding factor, or both. In What Works Clearinghouse (WWC) study reviews, certified reviewers look for a specific type of confounding factor: those that occur when a component of the study…

By creating and analyzing matched samples, researchers can simplify their analyses to include fewer covariate variables, relying less on model assumptions, and thus generating results that may be easier to report and interpret. When two groups essentially "look" the same, it is easier to explore their differences and make comparisons…

The What Works Clearinghouse (WWC) uses the term "baseline equivalence" when determining if the intervention group (those that received the intervention of interest) and the comparison group (those that did not receive the intervention) had characteristics that were similar enough ("equivalent") at the start of the study (at…

"Attrition" is the loss of sample during the course of a study. It occurs when individuals initially randomly assigned in a study are not included when researchers examine the outcome of interest. Attrition is a common issue in education research, and it occurs for many reasons. The What Works Clearinghouse (WWC) is an initiative of the…

Demonstration of experimental control is considered a hallmark of high-quality single-case research design (SCRD). Studies that fail to demonstrate experimental control may not be published because researchers are unwilling to submit these papers for publication and journals are unlikely to publish negative results (i.e., the file drawer effect).…

Rigorous scholarship is essential to the continued growth of group work, yet the unique nature of this counseling specialty poses challenges for quantitative researchers. The purpose of this proposal is to overview unique challenges to quantitative research with groups in the counseling field, including difficulty in obtaining large sample sizes…

A combination of behavioral and medication-based interventions has been the most effective form of treatment for reducing problem behavior in individuals with intellectual and developmental disabilities. Evaluating the 2 types of interventions in combination and separately may require that researchers adapt methods traditionally used to evaluate…

Given scarce resources for evaluation, we recommend that education researchers more frequently conduct comprehensive randomized trials that generate evidence on how, why, and under what conditions interventions succeed or fail in producing effects. Recent experience evaluating a randomized need-based financial aid intervention highlights some of…

In this article, the authors address the practicalities of how data should be presented, summarized, and interpreted. There are no exact rules; indeed there are valid concerns that exact rules may be inappropriate and too prescriptive. New procedures evolve, and new methods may be needed to deal with new types of data, just as people know that new…

The present paper describes the recruitment and site selection process that has been underway since January 2011, with particular emphasis on the use of Mahalanobis distance score to determine matched pairs of sites prior to randomization to treatment and control groups. Through a systematic winnowing process, the authors found that they could…

Educational researchers frequently study the impact of treatments or interventions on educational outcomes. However, when observational or quasiexperimental data are used for such investigations, selection bias can adversely impact researchers' abilities to make causal inferences about treatment effects. One way to deal with selection bias is to…

Education research rarely lends itself to large scale experimental research and true randomization, leaving the researcher to quasi-experimental designs. The problem with quasi-experimental research is that underlying factors may impact group selection and lead to potentially biased results. One way to minimize the impact of non-randomization is…

In this set of four supplemental tables, the authors compare the baseline test scores of the treatment and matched control group samples observed in each year after KIPP entry (outcome years 1 to 4). As discussed in Chapter III, the authors used an iterative propensity score estimation procedure to calculate each student's probability of entering…

Experimental designs are distinguished as the best method to respond to questions involving causality. The purpose of the present paper is to explicate the logic of experimental design and why it is so vital to questions that demand causal conclusions. In addition, types of internal and external validity threats are discussed. To emphasize the…