Statistical Guideline #2: Report Appropriate Reliability for your Sample, Measure, and Design
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INTEGRATIVE REVIEW
Statistical Guideline #2: Report Appropriate Reliability for your Sample, Measure, and Design Suzanne C. Segerstrom 1
# International Society of Behavioral Medicine 2019
Abstract From the Editors: This is the second column from the Statistics Guru. The Statistics Guru will appear in every issue. In these columns, we briefly discuss appropriate ways to analyze and present data in the journal. As such, the Statistics Guru can be seen both as an editorial amuse bouche and a set of guidelines for reporting data in the International Journal of Behavioral Medicine. If you have ideas for a column, please email the Statistical Editor, Suzanne Segerstrom at [email protected]. Keywords Statistical guidelines . Reliability . Generalizability
Introduction A frequent request from editors and reviewers is for authors to report the reliability of a scale in their sample. The second statistical guideline for IJBM is for authors to provide this report for every measure. “Reliability is not a property of a test per se, but rather a property of a scale applied in a given context to a particular population” ([1], p. 401). Even within a population, reliability is subject to sampling variability. That is, scale reliability in a sample of adolescents may not be reproduced in older adults or even in a different sample of adolescents. Informed interpretation of statistical analyses relies on scale reliability obtained in the sample under consideration. In addition, authors should consider reliabilities other than Cronbach’s alpha, reliability of change in a scale over
This is one in a series of statistical guidelines designed to highlight common statistical considerations in behavioral medicine research. The goal is to briefly discuss appropriate ways to analyze and present data in the International Journal of Behavioral Medicine (IJBM). Collectively, the series will culminate in a set of basic statistical guidelines to be adopted by IJBM and integrated into the journal’s official Instructions for Authors, and also to serve as an independent resource. If you have ideas for a future topic, please email the Statistical Editor, Suzanne Segerstrom at [email protected]. * Suzanne C. Segerstrom [email protected] 1
Department of Psychology, University of Kentucky, 125 Kastle Hall, Lexington, KY 40506-0044, USA
time, and reliability ensuing from the consolidation of repeated measurements and report them if applicable. The general definition of scale reliability from classical test theory is the ratio of true score variance to scale score variance; thus, higher reliability suggests a higher proportion of the obtained score due to the (unobserved) true score. Most authors report Cronbach’s alpha for scales with continuous responses, which seem to comprise the majority of psychological scales (scales with binary responses can be characterized with KuderRichardson formula 20 reliability). Alpha is a function of item interrelatedness and the number of items in the scale. Note that alpha is not a measure of internal consiste
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