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ERIC Number: EJ1115258
Record Type: Journal
Publication Date: 2016
Pages: 14
Abstractor: As Provided
ISSN: ISSN-1934-5747
Designing Intervention Studies: Selected Populations, Range Restrictions, and Statistical Power
Miciak, Jeremy; Taylor, W. Pat; Stuebing, Karla K.; Fletcher, Jack M.; Vaughn, Sharon
Journal of Research on Educational Effectiveness, v9 n4 p556-569 2016
An appropriate estimate of statistical power is critical for the design of intervention studies. Although the inclusion of a pretest covariate in the test of the primary outcome can increase statistical power, samples selected on the basis of pretest performance may demonstrate range restriction on the selection measure and other correlated measures. This can result in attenuated pretest-posttest correlations, reducing the variance explained by the pretest covariate. We investigated the implications of two potential range restriction scenarios: direct truncation on a selection measure and indirect range restriction on correlated measures. Empirical and simulated data indicated that direct range restriction on the pretest covariate greatly reduced statistical power and necessitated sample size increases of 82%-155% (dependent on selection criteria) to achieve equivalent statistical power to parameters with unrestricted samples. However, measures demonstrating indirect range restriction required much smaller sample size increases (32%-71%) under equivalent scenarios. Additional analyses manipulated the correlations between measures and pretest-posttest correlations to guide planning experiments. Results highlight the need to differentiate between selection measures and potential covariates and to investigate range restriction as a factor impacting statistical power.
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Publication Type: Journal Articles; Reports - Research
Education Level: Elementary Education; Grade 4; Intermediate Grades
Audience: N/A
Language: English
Sponsor: Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) (NIH)
Authoring Institution: N/A
Identifiers - Assessments and Surveys: Gates MacGinitie Reading Tests
Grant or Contract Numbers: P50HD052117