We demonstrated that the PEG, an ultra-brief three-item scale derived from the BPI, was a reliable and valid measure of pain among primary care patients with chronic musculoskeletal pain and diverse VA ambulatory patients. The PEG appears comparable to the BPI in terms of responsiveness to change. These findings support our hypothesis that an abbreviated scale derived from the BPI may be both useful and practical for chronic pain assessment in primary care and other ambulatory care settings, such as medical and surgical specialty clinics.
Strengths of this study include the confirmation of reliability and validity in an independent patient population, the diversity of the study populations, and the availability of multiple pain and functional measures with which to assess construct validity. Our choice of the BPI as the basis for our abbreviated scale development is another strength. The BPI is a widely used instrument that has been validated in numerous patient populations, clinical settings, and languages. BPI items are rated from 0–10, a format that has become familiar to patients and clinicians since assessment of pain with numeric scales has been broadly implemented in US health care settings. We took advantage of our collective experience with the BPI in observational and interventional research by employing a consensus-based process for scale shortening, consistent with recommendations to avoid over-reliance on statistical techniques.29
We believe our use of two different ambulatory study populations is a strength; however, each study has its own limitations. Study 1 was a sample of patients with chronic back and lower extremity musculoskeletal pain and included an over-representation of patients with depression (50% by design). The more clinically diverse patient population of Study 2, including ambulatory VA patients with and without chronic pain, enhances the generalizability of our findings. However, Study 2 included fewer pain measures with which to assess construct validity and was cross-sectional; therefore, we were able to assess responsiveness only in the first sample. Forty percent of Study 1 patients and 100% of Study 2 patients were recruited from VA clinics, so our findings may be less generalizable to non-VA settings.
We found that the PEG differentiated well between patients who improved and those who did not. According to responsiveness metrics, patients in the improved category had a large improvement in PEG score, whereas those in the unchanged category had a minimal change. Proper interpretation of the magnitude of change according to SRM and one group pre-post ES is not entirely clear, although authors have suggested that Cohen’s definition of small (0.2), moderate (0.5), and large (0.8) effects can be applied to interpretation of both responsiveness measures.36,37
We did not find evidence of PEG responsiveness in the worse direction (i.e., change scores between those who were unchanged and those who were worse did not significantly differ). We are limited in our ability to adequately assess sensitivity to worsening because we evaluated responsiveness in a single study population that likely had a ceiling effect for worsening due to high baseline pain severity.
The competing demands of primary care, in which visits are short and pain is only one of several problems warranting attention, make efficiency of assessment a paramount concern.38,39
A balance must be found between feasibility and key characteristics such as reliability, validity, and responsiveness. For example, ultra-brief depression measures containing two to three items perform better than single item depression measures.40
We also evaluated a four-item abbreviated scale, but found that adding an item contributed little. An abbreviated version of the BPI that eliminated a few items has been previously published,41
but the PEG is the first ultra-brief scale based on the BPI.
New assessment strategies are needed to support improved chronic pain management in primary care. We believe the PEG, which includes items assessing pain intensity, emotional function, and physical function, is an important step forward. However, further studies are needed to confirm our findings and validate the PEG in additional patient populations. Prospective research should determine whether serial pain measurement can improve the quality of clinical decision-making and pain outcomes in primary care. Given the huge clinical and societal burden associated with pain, developing efficient and effective strategies to enhance care is an important priority.