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ERIC Number: EJ1106857
Record Type: Journal
Publication Date: 2016-Aug
Pages: 28
Abstractor: As Provided
Reference Count: 21
ISBN: N/A
ISSN: ISSN-1076-9986
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.
SAGE Publications. 2455 Teller Road, Thousand Oaks, CA 91320. Tel: 800-818-7243; Tel: 805-499-9774; Fax: 800-583-2665; e-mail: journals@sagepub.com; Web site: http://sagepub.com
Publication Type: Journal Articles; Reports - Evaluative
Education Level: N/A
Audience: N/A
Language: English
Sponsor: Institute of Education Sciences (ED)
Authoring Institution: N/A
IES Funded: Yes
Grant or Contract Numbers: R305B090023; R305B100027