This protocol guided the review of research that informs the What Works Clearinghouse (WWC) practice guide entitled "Strategies for Postsecondary Students in Developmental Education -- A Practice Guide for College and University Administrators, Advisors, and Faculty." This protocol was used in conjunction with the "WWC Procedures…

The use of singular methodologies has dominated emotional and behavioral disorder (EBD) intervention research, and by extension, the field has not deployed mixed-methods research (MMR). The purpose of this article is to provide an overview of MMR and demonstrate its utility for conducting EBD intervention research. The basic tenants and design…

Postelection surveys regularly overestimate voter turnout by 10 points or more. This article provides the first comprehensive documentation of the turnout gap in three major ongoing surveys (the General Social Survey, Current Population Survey, and American National Election Studies), evaluates explanations for it, interprets its significance, and…

"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…

This brief paper introduces a new approach to assessing the trustworthiness of research comparisons when expressed numerically. The 'number needed to disturb' a research finding would be the number of counterfactual values that can be added to the smallest arm of any comparison before the difference or 'effect' size disappears, minus the number of…

Large-scale randomized studies provide the best means of evaluating practical, replicable approaches to improving educational outcomes. This article discusses the advantages, problems, and pitfalls of these evaluations, focusing on alternative methods of randomization, recruitment, ensuring high-quality implementation, dealing with attrition, and…

Background: The Education Endowment Foundation (EEF) is an independent charity that was established in 2011 with the explicit aim of breaking the link between family income and educational achievement in England. Over the seven years since its inception, EEF has contributed to the existing evidence base by funding over one hundred randomised…

The What Works Clearinghouse (WWC) Standards Briefs explain the rules the WWC uses to evaluate the quality of studies for practitioners, researchers, and policymakers. Attrition (loss of sample) occurs when individuals initially included in a study are not included in the final study analysis. Attrition is a common issue in education research and…

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…

This review protocol from the What Works Clearinghouse (WWC) covers the following issues relevant to screening criteria and full review for the Access to Higher Education Practice Guide: (1) time frame; (2) study design; (3) age and/or grade range; (4) brief description of intervention; (5) key subgroups; (6) location and language; (7) outcomes…

Meeting the What Works Clearinghouse (WWC) attrition standard (or one of the attrition standards based on the WWC standard) is now an important consideration for researchers conducting studies that could potentially be reviewed by the WWC (or other evidence reviews). Understanding the basis of this standard is valuable for anyone seeking to meet…

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…

Recruitment and retention of research participants is evolving with the changing demographics of the American population, in particular its growing diversity. The cultural-historical background and sociopolitical conditions of each diverse group poses unique challenges in developing successful recruitment and retention methods and strategies. This…

The past decade has seen a noticeable shift in missing data handling techniques that assume a missing at random (MAR) mechanism, where the propensity for missing data on an outcome is related to other analysis variables. Although MAR is often reasonable, there are situations where this assumption is unlikely to hold, leading to biased parameter…

This addendum to previously published results presents alternative analyses of data from large-scale effectiveness studies of Cognitive Tutor Algebra I in middle schools and high schools. These alternative analyses produce results that are substantively the same as previously reported. We find a significant positive effect of 0.21 standard…