Objective: The study investigated the test-retest reliability and construct validity of the Global Perceived Effect (GPE) scale in patients with musculoskeletal disorders.
Study design and setting: Data from seven clinical studies including 861 subjects were used for the analyses. Repeat measures taken at the same attendance and from attendances separated by 24 hours were compared to estimate test-retest reliability. Construct validity was evaluated by examining relationships between pre, post, and change scores in pain and disability measures with GPE measures.
Results: Intraclass correlation coefficient values of 0.90-0.99 indicate excellent reproducibility of the GPE scale. In all but one data set, change scores on pain and disability measures correlated well (r=0.40-0.74) with GPE; however, post scores nearly always correlated even more strongly (r=0.58-0.84), and pre scores showed much weaker association (r=0.00-0.28). Pre scores accounted for only a small amount of additional R(2) when added to regression models including post score.
Conclusions: Test-retest reliability of the GPE is excellent. GPE ratings are strongly influenced by current status, with the effect more obvious as transition time lengthens. This result questions whether transition ratings truly reflect change, or rather just current state. This finding also has implications for the use of GPE ratings as an external criterion of change in clinimetric studies.
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