Article

Objective: To provide a practical guide on how to avoid the pitfalls of correlated correlation coefficients when comparing multiple instruments in rehabilitation research. Design: An observational study comparing a number of instruments measuring quality of life (QoL) compared with an external criterion. Subjects: Sixty-eight patients admitted to a rheumatology ward for intensive treatment of rheumatoid arthritis. Methods: Patients completed three new ( QoL) instruments and an established instrument before and after intensive treatment for rheumatoid arthritis. Main outcome measures: Correlation coefficients together with their confidence intervals and a test for the difference between a set of correlated correlation coefficients for the change in the EuroQoL Quality of Life scale ( EuroQoL), the World Health Organization Quality Of Life-Abbreviated version (WHOQoL-BREF) and the Quality of Life Profile (QLP) against the Stanford Health Assessment Questionnaire (HAQ). Results: Although the range of correlation between the new instruments and the external criterion was between - 0.37 and - 0.59 and suggested that one new instrument was far more responsive than the others,; an omnibus test for an overall difference could find no difference in responsiveness. Conclusions: It is conceptually simple to use correlation coefficients to assess the properties of multiple instruments measured on the same subjects to find a 'best' instrument. However, proper interpretation of results when correlated correlation coefficients are calculated is complex. We recommend analysis includes: ( a) that simple plots of the pairs of analysed variables are shown, (b) that simple linear model-fitting statistics, e. G., the R-squared statistic, accompany the plots, ( c) that confidence intervals are presented for correlation coefficients, (d) that an omnibus statistical test for the difference between correlated correlation coefficients is presented, and ( e) that normal model assumptions are tested.

Langue : ANGLAIS