Title: | What to Do When Data Are Missing in Group Randomized Controlled Trials |
Description: | This NCEE Technical Methods report examines how to address the problem of missing data in the analysis of data in Randomized Controlled Trials (RCTs) of educational interventions, with a particular focus on the common educational situation in which groups of students such as entire classrooms or schools are randomized. Missing outcome data are a problem for two reasons: (1) the loss of sample members can reduce the power to detect statistically significant differences, and (2) the introduction of non-random differences between the treatment and control groups can lead to bias in the estimate of the interventionfs effect. The report reviews a selection of methods available for addressing missing data, and then examines their relative performance using extensive simulations that varied a typical educational RCT on three dimensions: (1) the amount of missing data; (2) the level at which data are missingat the level of whole schools (the assumed unit of randomization) or for students within schools; and, (3) the underlying missing data mechanism. The performance of the different methods is assessed in terms of bias in both the estimated impact and the associated standard error. |
Online Availability: | |
Cover Date: | October 2009 |
Web Release: | October 13, 2009 |
Print Release: | October 13, 2009 |
Publication #: | NCEE 20090049 General Ordering Information |
Center/Program: | NCEE |
Authors: | Michael J. Puma: Chesapeake Research Associates, LLC; Robert B. Olsen, Stephen H. Bell, and Cristofer Price: Abt Associates, Inc. |
Type of Product: | Technical Methods Report |
Keywords: | |
Questions: | For questions about the content of this Technical Methods Report, please contact the Webmaster. |