The Impact of Covariates on Statistical Power in Cluster Randomized Designs: Which Level Matters More?

Autor/in	Konstantopoulos, Spyros
Titel	The Impact of Covariates on Statistical Power in Cluster Randomized Designs: Which Level Matters More?
Quelle	In: Multivariate Behavioral Research, 47 (2012) 3, S.392-420 (29 Seiten) PDF als Volltext Verfügbarkeit
Sprache	englisch
Dokumenttyp	gedruckt; online; Zeitschriftenaufsatz
ISSN	0027-3171
DOI	10.1080/00273171.2012.673898
Schlagwörter	Statistical Analysis; Multivariate Analysis; Robustness (Statistics); Class Size; Grade 3; Elementary School Students; Academic Achievement + Suchen Sie Ihr Suchwort? Statistische Analyse; Multivariate Analyse; Widerstandsfähigkeit; Klassengröße; School year 03; 3. Schuljahr; Schuljahr 03; Schulleistung
Abstract	Field experiments with nested structures are becoming increasingly common, especially designs that assign randomly entire clusters such as schools to a treatment and a control group. In such large-scale cluster randomized studies the challenge is to obtain sufficient power of the test of the treatment effect. The objective is to maximize power without adding many clusters that make the study much more expensive. In this article I discuss how power estimates of tests of treatment effects in balanced cluster randomized designs are affected by covariates at different levels. I use third-grade data from Project STAR, a field experiment about class size, to demonstrate how covariates that explain a considerable proportion of variance in outcomes increase power significantly. When lower level covariates are group-mean centered and clustering effects are larger, top-level covariates increase power more than lower level covariates. In contrast, when clustering effects are smaller and lower level covariates are grand-mean centered or uncentered, lower level covariates increase power more than top-level covariates. (Contains 6 tables.) (As Provided).
Anmerkungen	Psychology Press. Available from: Taylor & Francis, Ltd. 325 Chestnut Street Suite 800, Philadelphia, PA 19106. Tel: 800-354-1420; Fax: 215-625-2940; Web site: http://www.tandf.co.uk/journals
Erfasst von	ERIC (Education Resources Information Center), Washington, DC
Update	2017/4/10