Use of the Standard Error as a Reliability Index of Interest: An Applied Example Using Elbow Flexor Strength Data

The intraclass correlation coefficient (ICC) and the standard error of measurement (SEM) are two reliability coefficients that are reported frequently. Both measures are related; however, they define distinctly different properties. The magnitude of the ICC defines a measure's ability to discri...

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Bibliographic Details
Published in:Physical therapy 1997-07, Vol.77 (7), p.745-750
Main Authors: Stratford, P W, Goldsmith, C H
Format: Article
Language:English
Subjects:
Analysis
Analysis of Variance
Bias
Confidence Intervals
Data Interpretation, Statistical
Elbow
Elbow Joint - physiology
Female
Humans
Joints
Kinetics
Physical Therapy Modalities
Range of motion
Reliability
Reproducibility of Results
Statistical analysis
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Summary:The intraclass correlation coefficient (ICC) and the standard error of measurement (SEM) are two reliability coefficients that are reported frequently. Both measures are related; however, they define distinctly different properties. The magnitude of the ICC defines a measure's ability to discriminate among subjects, and the SEM quantifies error in the same units as the original measurement. Most of the statistical methodology addressing reliability presented in the physical therapy literature (eg, point and interval estimations, sample size calculations) focuses on the ICC. Using actual elbow flexor make and break strength measurements, this article illustrates a method for estimating a confidence interval for the SEM, shows how an a priori specification of confidence interval width can be used to estimate sample size, and provides several approaches for comparing error variances (and square root of the error variance, or the SEM).
ISSN:0031-9023
1538-6724
DOI:10.1093/ptj/77.7.745