PROMIS Physical Function Short Forms Display Item- and Scale-Level Characteristics at Least as Good as the Roland Morris Disability Questionnaire in Patients With Chronic Low Back Pain

Publication date: February 2020

Source: Archives of Physical Medicine and Rehabilitation, Volume 101, Issue 2

Author(s): Alessandro Chiarotto, Leo D. Roorda, Martine H. Crins, Maarten Boers, Raymond W. Ostelo, Caroline B. Terwee

Abstract

Objective

To compare dimensionality, item-level characteristics, scale-level reliability, and construct validity of PROMIS Physical Function short forms (PROMIS-PF) and 24-item Roland Morris Disability Questionnaire (RMDQ-24) in patients with chronic low back pain (LBP).

Design

Cross-sectional study.

Setting

Secondary care center for rehabilitation and rheumatology.

Participants

Patients with nonspecific LBP ≥3 months (N=768). Mean age was 49±13 years, 77% were female, and 54% displayed pain for more than 5 years.

Interventions

Not applicable.

Main Outcome Measures

Dutch versions of the 4-, 6-, 8-, 10-, and 20-item PROMIS-PF and of the RMDQ-24.

Results

PROMIS-PF-6, PROMIS-PF-8, and RMDQ-24 exhibited sufficient unidimensionality (confirmatory factor analysis: comparative fit index>0.950, Tucker-Lewis index>0.950, root means square error of approximation<0.060), whereas the other instruments did not. All instruments were free of local dependence except PROMIS-PF-20 with 4 item pairs with clear residual correlations. Mokken scale analysis found 1 nonmonotone item for PROMIS-PF-20 and 8 for RMDQ-24 (ie, the probability of endorsing these items was not increasing with increasing level on the underlying construct). PROMIS-PF-20 displayed 2 misfitting items (S-χ² P value>.001). Two-parameter item response theory models found 2 items with low discrimination for RMDQ-24. All other instruments had adequate fit statistics and item parameters. PROMIS-PF-20 displayed the best scale-level reliability. Construct validity was sufficient for all instruments as all hypotheses on expected correlations with other instruments and differences between relevant subgroups were met.

Conclusions

PROMIS-PF-6, PROMIS-PF-8, and RMDQ-24 exhibited better unidimensionality, whereas PROMIS-PF-4, PROMIS-PF-6, PROMIS-PF-8, and PROMIS-PF-10 showed superior item-level characteristics. PROMIS-PF-20 was the instrument with the best scale-level reliability. This study warrants assessment of other measurement properties of PROMIS-PF short forms in comparison with disease-specific physical functioning instruments in LBP.

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