Convergent and Discriminative Validity of the PROMIS Physical Function 4 Questionnaire for Assessing Pain-Related Disability in Low Back Pain Patients Seeking Chiropractic Care

Sandal LF1, Young JJ1,2, Søgaard K1, Hartvigsen J1,3 1UniversityofSouthernDenmark, 2CanadianMemorialChiropracticCollege, 3ChiropracticKnowledgeHub,Odense,Denmark

Abstract

Study Design

A prospective cohort study.

Objective

To investigate construct validity by examining the convergent and discriminative validity of the Patient-Reported Outcomes Measurement Information System Physical Function 4a (PROMIS-PF4) questionnaire in low back pain (LBP) patients seeking care from Danish chiropractors.

Summary of Background Data

The Roland-Morris Disability Questionnaire (RMDQ) is often used to assess physical functioning in LBP. However, it consists of 24 items, which is time consuming to complete in clinical practice. The PROMIS-PF4 questionnaire has only four items and may be more applicable for clinical use.

Materials and Methods

Patients with LBP seeking care from chiropractors in Denmark completed the PROMIS-PF4, RMDQ, Subgroups for Targeted Treatment (STarT) Back screening tool, and Numeric Pain Rating Scale (NPRS) in advance of their first appointment with the chiropractor. Convergent validity was assessed using Spearman correlation coefficients between the PROMIS-PF4 and RMDQ and NPRS, respectively. Discriminative validity of the PROMIS-PF4 was assessed by calculating the area under the receiver operating characteristic curve (AUC) when plotting the PROMIS-PF4 t score against a reference case for RMDQ; NPRS; and high and low risk groups using the STarT Back screening tool.

Results

Among 356 patients the PROMIS-PF4 questionnaire had strong convergent validity with the RMDQ (r=−0.76) and moderate convergent validity with the NPRS (r=−0.42). The PROMIS-PF4 had good and acceptable discriminative validity for disability (AUC=0.88) and high risk of persisting disability (AUC=0.72), and poor or no discriminative validity for pain intensity (AUC=0.66) and low-risk of persisting disability (AUC=0.26), respectively.

Conclusion

As hypothesized, for convergent validity the PROMIS-PF4 has stronger correlation with the RMDQ than the NPRS and good discriminative validity for identifying patients with pain-related disability and at high risk of persisting disability but not for identifying pain intensity or low-risk of persisting disability. Consequently, the PROMIS-PF4 has adequate construct validity for measuring pain-related disability in an LBP population in chiropractic care.

Valid measurement tools are important in research to identify and characterize patient populations and to evaluate change in health outcome and symptom state in a clinical setting. Equally important is to have easily administered patient-reported outcomes that can be used as screening tools in research and clinical settings. For low back pain (LBP) research, the core set of outcomes include measures of physical functioning, pain intensity, and health-related quality of life.1,2 For physical functioning, the Roland-Morris Disability Questionnaire (RMDQ),3,4 (www. rmdq.org) and the Oswestry Disability Index (ODI)5,6 are recommended and widely used.1 However, both the RMDQ (23/24 items, answered yes/no) and the ODI (10 items, five answer categories) are time consuming to complete, and length of questionnaires is known to negatively affect response rates.7

The National Institutes of Health (NIH) developed the Patient-Reported Outcomes Measurement Information System (PROMIS), (https://www.healthmeasures.net/) to develop and evaluate a set of publicly available, efficient and flexible measurement of patient reported outcomes.8 PROMIS contains three overarching domains: mental, social and physical health, the latter including a subdomain for Physical Function (PF).8 The PROMIS-PF item bank consists of a total of 124 items,8 from which several questionnaires (PF20, PF10, PF8, PF6, and PF4) have been created.9,10 This study concerns the PROMISPF4 questionnaire, which assesses physical function using only four items. While the reliability and validity for several of the PROMIS-PF questionnaires has been investigated in other populations,8 it is understudied in people with LBP.1

This study investigates the construct validity of the PROMIS-PF4 for measuring pain-related disability in people with LBP seeking care from chiropractors by (1) examining the convergent validity of the PROMIS-PF4 questionnaire against patient reported outcomes for painrelated disability and pain intensity and (2) examining the discriminative validity of the questionnaire against known groups. For convergent validity, we hypothesize a stronger correlation between the PROMIS-PF4 and pain-related disability, measured by the RMDQ, compared with between the PROMIS-PF4 and pain intensity, measured by the Numerical Pain Rating Scale (NPRS), as both PROMIS-PF4 and RMDQ assess a physical function construct, whereas the NPRS measures a pain intensity construct. For discriminative validity, we hypothesize that the PROMISPF4 better identifies patients with high pain-related disability or at high risk of disability and hypothesize lower validity for identification of patients at low-risk of disability or high pain intensity.

OriginallypublishedinSpine,2022Sep15;47(18):13141320

ReproducedwithpermissionfromWolter’sKluwerHealthInc.

Access online: doi:10.1097/BRS.0000000000004391