Background/Context: Attrition has been described as "the Achilles Heel of the randomized experiment" (Shadish et al., 1998 p.3). Attrition looms as a threat because it can undermine group equivalence, eroding the methodological strength at the heart of a randomized evaluation. In particular, attrition could result in unobserved…

Evaluators of education interventions are increasingly designing studies to detect impacts much smaller than the 0.20 standard deviations that Cohen characterized as "small." While the need to detect smaller impacts is based on compelling arguments that such impacts are substantively meaningful, the drive to detect smaller impacts may…

Respondent attrition is a common problem in national longitudinal panel surveys. To make full use of the data, weights are provided to account for attrition. Weight adjustments are based on sampling design information and data from the base year; information from subsequent waves is typically not utilized. Alternative methods to address bias from…

Most longitudinal studies are plagued by drop-out related to variables at earlier assessments (systematic attrition). Although systematic attrition is often analysed in longitudinal studies, surprisingly few researchers attempt to reduce biases due to systematic attrition, even though this is possible and nowadays technically easy. This is…

Evaluators of education interventions are increasingly designing studies to detect impacts much smaller than the 0.20 standard deviations that Cohen (1988) characterized as "small." While the need to detect smaller impacts is based on compelling arguments that such impacts are substantively meaningful, the drive to detect smaller impacts…

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…

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…

Instability in the school population between school entrance and school leaving is not "just a problem of missing data" but often the visible result of the educational problems in some schools and is, therefore, not merely to be treated as missing data but as indicator for the quality of educational processes. Even the most superior…

This technical paper examines the issue of attrition bias in two cohorts of the Longitudinal Surveys of Australian Youth (LSAY), based on an analysis using data from 1995 to 2002. Data up to 2002 provided eight years of information on members of the Y95 cohort and five years of information on members of the Y98 cohort. This study suggests that…

Presents a method for the collection and analysis of collateral data about research subjects (i.e., measurements of events in subjects' lives that may affect outcome measures and/or lead to attrition). A six-step procedure evaluates bias resulting from subject attrition from a study using data from lost and retained subjects. (SLD)

Presents procedures for reducing attrition in clinical research and provides a case study for examination by researchers. Includes lists of preventative strategies and statistical methodologies to reduce attrition and bias. Argues that early planning for attrition by adjusting sample sizes is a scientifically sound approach to clinical research…

The bias attributable to nonresponse in population estimates in the field of education was studied. Data were collected from responses to mathematics and science exercises administered by the National Assessment of Educational Progress to a probability sample of 17-year olds, as well as a probability sample selected from nonrespondents.…

Bias due to attrition of respondents poses a threat to the internal and external validity of research findings. Discusses methods of detecting attrition bias in longitudinal family research, and presents Heckman's procedure to correct attrition bias. Data from the University of California Longitudinal Study of Generations are used to illustrate…

A strategy proposed by T. Cook and D. Campbell (1979) was used to investigate attrition in a community-based literacy program, focusing on 287 Head Start families. Data revealed interactions among intervention program-centered characteristics and person-centered characteristics that have implications for study validity and generalizability.…