ERIC Number: EJ1106857
Record Type: Journal
Publication Date: 2016-Aug
Abstractor: As Provided
Reference Count: 21
On the Hedges Correction for a "t"-Test
VanHoudnos, Nathan M.; Greenhouse, Joel B.
Journal of Educational and Behavioral Statistics, v41 n4 p392-419 Aug 2016
When cluster randomized experiments are analyzed as if units were independent, test statistics for treatment effects can be anticonservative. Hedges proposed a correction for such tests by scaling them to control their Type I error rate. This article generalizes the Hedges correction from a posttest-only experimental design to more common designs used in practice. We show that for many experimental designs, the generalized correction controls its Type I error while the Hedges correction does not. The generalized correction, however, necessarily has low power due to its control of the Type I error. Our results imply that using the Hedges correction as prescribed, for example, by the What Works Clearinghouse can lead to incorrect inferences and has important implications for evidence-based education.
Descriptors: Statistical Analysis, Randomized Controlled Trials, Error of Measurement, Scaling, Research Design, Statistical Inference, Meta Analysis, Equations (Mathematics), Effect Size, Evidence Based Practice, Hierarchical Linear Modeling
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