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Download full textWhat Works Clearinghouse, 2017
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…
Descriptors: Research Methodology, Intervention, Control Groups, Experimental Groups
What Works Clearinghouse, 2017
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…
Descriptors: Control Groups, Experimental Groups, Intervention, Comparative Analysis
What Works Clearinghouse, 2017
"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…
Descriptors: Attrition (Research Studies), Control Groups, Experimental Groups, Randomized Controlled Trials
What Works Clearinghouse, 2015
The What Works Clearinghouse (WWC) Standards Briefs explain the rules the WWC uses to evaluate the quality of studies for practitioners, researchers, and policymakers. This brief explains what baseline equivalence is and why it matters. As part of the WWC review process for certain types of studies, reviewers assess whether the intervention group…
Descriptors: Control Groups, Participant Characteristics, Matched Groups, Research Methodology
What Works Clearinghouse, 2014
Attrition occurs when members of the initial research sample are not part of the final analysis sample, such as due to missing data or leaving the study. Both the overall sample attrition and the differences in attrition between the groups can affect the statistical equivalence of the sample and create potential for bias. The WWC has given careful…
Descriptors: Attrition (Research Studies), Statistical Bias, Randomized Controlled Trials, Models
What Works Clearinghouse, 2013
Attrition occurs when members of the initial research sample are not part of the final analysis sample, such as due to missing data or leaving the study. Both the overall sample attrition and the differences in attrition between the groups can affect the statistical equivalence of the sample and create potential for bias. The WWC has given careful…
Descriptors: Attrition (Research Studies), Statistical Bias, Randomized Controlled Trials, Models
