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Power Estimates in the Presence of a Covariate and Measurement Error

University of British Columbia

Kenneth D. Hopkins

University of Colorado

The statistical power of a test of significance for the difference among means is dependent upon a number of factors, among them the presence of a covariate, which often serves to increase power, as well as measurement error, which reduces power. Formulas are provided for adjusting Cohen's (1977) f value for these two sources of variability. These adjusted f values can then be used with Cohen's power tables. An example of the use of these formulas in the planning stage of a study is given, followed by a description of the complex nature of the relationship between power and covariance and measurement error.

Educational and Psychological Measurement, Vol. 48, No. 3, 647-656 (1988)
DOI: 10.1177/0013164488483008


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