The Two Errors of Using the Within-Subject Standard Deviation (WSD) as the Standard Error of a Reliable Change Index

In this Journal, Lewis and colleagues introduced a new Reliable Change Index (RCIWSD), which incorporated the within-subject standard deviation (WSD) of a repeated measurement design as the standard error. In this note, two opposite errors in using WSD this way are demonstrated. First, being the sta...

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Bibliographic Details
Published in:Archives of clinical neuropsychology 2010-08, Vol.25 (5), p.451-456
Main Author: Maassen, Gerard H
Format: Article
Language:English
Subjects:
Data Interpretation, Statistical
Humans
Neuropsychological Tests - statistics & numerical data
Outcome and Process Assessment (Health Care) - statistics & numerical data
Psychometrics
reliable change index
Reproducibility of Results
standard error
within-subject standard deviation
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Summary:In this Journal, Lewis and colleagues introduced a new Reliable Change Index (RCIWSD), which incorporated the within-subject standard deviation (WSD) of a repeated measurement design as the standard error. In this note, two opposite errors in using WSD this way are demonstrated. First, being the standard error of measurement of only a single assessment makes WSD too small when practice effects are absent. Then, too many individuals will be designated reliably changed. Second, WSD can grow unlimitedly to the extent that differential practice effects occur. This can even make RCIWSD unable to detect any reliable change.
ISSN:0887-6177
1873-5843
DOI:10.1093/arclin/acq036