We used data from two sources: 1) Stepped Care for Affective Disorders and Musculoskeletal Pain (SCAMP), a longitudinal study that enrolled a total of 500 patients with chronic musculoskeletal pain, and 2) Helping Veterans Experience Less Pain (HELP-vets), a cross-sectional study of 646 veterans receiving care at VA clinics. We used data from Study 1 to develop and initially validate the ultra-brief measure and data from Study 2 to confirm reliability and validity in an independent patient population.
Study 1 (SCAMP) enrolled 500 primary care patients with persistent back, hip, or knee pain of at least moderate severity, 250 of whom had concurrent depression.18 Participants were recruited from university (n = 300) and VA-affiliated (n = 200) internal medicine clinics in Indianapolis. Patients with concurrent depression were enrolled in a trial of depression and pain treatment vs. usual care (n = 250). Those without depression were followed in a parallel observational study (n = 250). The mean age of SCAMP participants was 59 years; 52% were women, 58% were white, and 38% were black. The mean numeric rating of current pain (on a 0–10 scale) was 6.1 (SD 1.9) at baseline.
Study 2 (HELP-vets) enrolled a random visit-based sample of 646 veterans from ambulatory care clinics at two VA hospitals and six affiliated community sites in three urban California counties. Patients with chronic illness were over-sampled by design. The mean age was 63 years and 95% were male. Self-reported race/ethnicity was 54% white, 30% black, and 10% Latino. Sixty-one percent of participants reported pain at the time of enrollment and 63% had one or more pain diagnoses (33% back pain, 45% other musculoskeletal pain, 12% neuropathic pain, 5% headache). The mean rating of current pain (on a 0–10 scale) was 3.1 (SD 3.2) overall and 5.1 (SD 2.6) among those with pain.
Study 1 participants completed the BPI, Chronic Pain Grade questionnaire (CPG), Roland disability scale, and SF-36 bodily pain scale at baseline; they completed the BPI, CPG, and pain global rating of change at 6 months. Study 2 was cross-sectional; participants completed the BPI, Functional Morbidity Index, and a single-item rating of overall pain-related distress.
The Brief Pain Inventory (BPI) includes two scales that assess pain intensity and pain-related functional impairment (physical and emotional).13,15 The four items of the BPI severity scale assess the intensity of current pain and pain at its least, worst, and average during the past week on scales from 0 (“no pain”) to 10 (“pain as bad as you can imagine”). The BPI interference scale assesses pain-related functional interference with seven items assessing different domains (general activity, mood, walking ability, normal work, relations with other people, sleep, and enjoyment of life) rated from 0 (“does not interfere”) to 10 (“interferes completely”).
The Chronic Pain Grade questionnaire (CPG) includes two three-item scales (intensity and disability) that are transformed into 0–100 scores.19 An algorithm classifies pain into four graded categories: 1) low disability-low intensity, 2) low disability-high intensity, 3) high disability-moderately limiting, and 4) high disability-severely limiting. The CPG has been validated in primary care, chronic pain, and general populations.20–22
The Roland Disability questionnaire is a pain-specific measure of physical disability validated in patients with back pain and other chronic pain conditions.23,24 It includes a checklist of 24 statements about pain effects on function; the score is the number of items endorsed.
The Short-Form 36-item questionnaire (SF-36) Bodily Pain Scale is a two item scale assessing pain severity and interference.25,26 Responses are transformed into a 0–100 score.
The Pain Global Rating of Change is a single item assessing patients’ overall impression of change in their pain. Study 1 participants were asked whether their pain was worse, about the same, or better since the start of the study. Those who reported that pain was better were asked to rate the magnitude of improvement (a little, somewhat, moderately, a lot, or completely better). Global ratings of change may be more sensitive to improvement and better correlated with patient satisfaction than serial measures.27
The Functional Morbidity Index was developed to assess general functional status in older adults.28 Patients indicate whether they are able perform four different activities independently, and if not, whether the impairment is due to a health problem.
Overall Pain Distress is a single item: “How much did overall pain distress or bother you during the past week?” Response options are not at all, a little bit, somewhat, quite a bit, and very much.
We used a consensus-based process, drawing on a literature review, expert opinion, and statistical data, to develop a shortened scale.29 Pre-specified criteria guided initial item selection. First, we decided to include at least one item representing each of three domains included in the BPI: pain intensity, physical functioning, and emotional functioning. We then selected items with the following characteristics: 1) easy to understand and applicable to patients with all types of pain; 2) good statistical characteristics (e.g., high response variability, high item-remainder correlation); 3) similar performance in depressed and non-depressed patients.
We chose “pain average” for the intensity item because it had a good distribution of responses, lacking the ceiling and floor effects seen with “pain worst” and “pain least,” respectively. We did not select “pain now” because we wanted to avoid duplicating information provided by the “fifth vital sign,” and capture intermittent pain. Although the ideal reporting period for pain assessment is debated, recalled average pain over one week is a valid measure of pain intensity.30,31
BPI interference items include those assessing physical status (general activity, walking, normal work), emotional status (mood, relations with others, enjoyment of life), and sleep. For physical interference, we chose “interference with general activity” because it applies equally to all patients, as opposed to “interference with work” (which may be affected by occupation, employment status, etc.) and “interference with walking” (which may not apply to non-ambulatory patients or those with upper body pain).
For emotional interference, we considered both “interference with mood” and “interference with enjoyment of life.” In our experience, “interference with relations with other people” is more difficult than other items for patients to answer. We wanted a scale that would discriminate between chronic pain and depression, which commonly co-occur.32 In our sample of patients with and without comorbid depression, we found that “interference with enjoyment of life” was more independent of depression than “interference with mood.” We also considered “interference with sleep” in place of the emotional interference items.
We reached consensus on a preferred three-item scale (“pain average,” “interference with enjoyment of life,” and “interference with general activity”) and alternative three-item and four-item scales, which we then evaluated statistically.
Reliability and Validity
We assessed reliability (internal consistency) by calculating Cronbach’s coefficient alpha. To assess construct validity, we compared the PEG with measures of pain and function using Pearson correlation coefficients. We used multiple measures for construct validity assessment, including the BPI, because no criterion standard exists for pain. We hypothesized that coefficients would be slightly higher for comparisons with pain-specific functional measures than for those with pain severity measures (because two of the three PEG items assess function). We also expected that coefficients would be larger for comparisons with pain-specific functional measures than for comparisons with generic functional measures.
Assessment of responsiveness, or sensitivity to change, requires an independent standard to define change.33 We used two different measurements to define the presence or absence of patient improvement: 1) global rating of change and 2) serial CPG grade. We categorized patients according to their pain trajectory as assessed by each of the two measures. Global rating of change categories were defined by the patient’s retrospective assessment at 6 months of the change in their pain since the trial began: 1) improved (“better”), 2) unchanged (“about the same”), and 3) worse (“worse”). CPG categories were defined by the change in CPG grade from baseline to 6 months: 1) improved (pain grade decreased by ≥1 level), 2) unchanged (pain grade at baseline = pain grade at follow-up), and 3) worse (pain grade increased by ≥1 level).
Using data from Study 1, we assessed responsiveness by calculating the following three metrics: 1) change score (difference between mean score at baseline and follow-up), 2) effect size (ES; change score divided by the standard deviation of the baseline score), and 3) standardized response mean (SRM; change score divided by the standard deviation of the change score). These calculations were performed for patients in the improved, unchanged, and worse categories. Confidence intervals for SRM were calculated as + /- 1.96 divided by the square root of the sample size.34 We assessed responsiveness using all three methods because they can produce differing results and because agreement is lacking on the preferred method.34,35 We compared responsiveness of the PEG, BPI severity and BPI interference scales by comparing ES and SRM for each measure among patients in the improved category. Finally, we assessed responsiveness to varying degrees of improvement by comparing change scores for PEG and BPI scales to degree of improvement by global rating of change.