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Sample Size Requirements for Precise Estimates of Reliability, Generalizability, and Validity Coefficients

Precision of the reliability coefficient (r) is investigated. The width of the confidence interval for r as a function of sample size (N) is shown for retest, alternate-form, split-half, alpha, intraclass, interrater, and validity coefficients. Although the determination of the N needed for reliabil...

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Bibliographic Details
Published in:Journal of clinical and experimental neuropsychology 1999-08, Vol.21 (4), p.559-566
Main Author: Charter, Richard A.
Format: Article
Language:English
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Summary:Precision of the reliability coefficient (r) is investigated. The width of the confidence interval for r as a function of sample size (N) is shown for retest, alternate-form, split-half, alpha, intraclass, interrater, and validity coefficients. Although the determination of the N needed for reliability studies is somewhat subjective, a minimum of 400 subjects is recommended. Much larger N s may be needed for validity studies. A survey of published reliability studies shows that 59% of the sample sizes were less than 100. Confidence intervals for obtained test scores are used as a practical application measure that also leads to the conclusion of a minimum of 400 subjects.
ISSN:1380-3395
1744-411X
DOI:10.1076/jcen.21.4.559.889