Table 2.
Means, Reliability, and Minimally Important Differences of Brief Pain Inventory and PEG Pain Scales in 6 Trials (n=1,710)
| Variable | SCAMP (n=427) | INCPAD (n=274) | SCOPE (n=250) | CAMEO (n=261) | SPACE (n=240) | SSM (n=258) |
|---|---|---|---|---|---|---|
| Population | Primary care | Oncology | Primary care | Primary care | Primary care | Post-Stroke |
| Mean (SD) | ||||||
| • BPI Severity | 5.7 (1.8) | 5.2 (1.8) | 5.1 (1.7) | 6.8 (1.6) | 5.6 (1.4) | 2.9 (2.8) |
| • BPI Interference | 5.8 (2.4) | 5.7 (2.6) | 5.3 (2.2) | 6.4 (2.1) | 5.5 (1.9) | 2.7 (3.0) |
| • BPI Total | 5.7 (2.0) | 5.5 (2.1) | 5.2 (1.8) | 6.5 (1.8) | 5.5 (1.6) | 2.8 (2.8) |
| • PEG | 6.0 (2.2) | 5.9 (2.2) | 5.4 (2.0) | 6.5 (1.9) | 5.8 (1.7) | 2.9 (3.0) |
| Cronbach’s alpha internal reliability | ||||||
| • BPI Severity | 0.83 | 0.79 | 0.87 | 0.79 | 0.84 | 0.86 |
| • BPI Interference | 0.87 | 0.89 | 0.88 | 0.86 | 0.85 | 0.94 |
| • BPI Total | 0.88 | 0.89 | 0.91 | 0.87 | 0.87 | 0.94 |
| • PEG | 0.73 | 0.69 | 0.76 | 0.72 | 0.79 | 0.85 |
| Anchor-Based MIDs | ||||||
| A Little Better* | ||||||
| • BPI Severity | 1.36 | -- | 0.73 | 0.87 | 1.17 | −0.39 |
| • BPI Interference | 2.02 | -- | 1.34 | 1.41 | 1.67 | −0.52 |
| • BPI Total | 1.82 | -- | 1.04 | 1.26 | 1.48 | −0.55 |
| • PEG | 2.05 | -- | 1.25 | 1.18 | 2.02 | −0.52 |
| Distribution-Based MIDs | ||||||
| 0.35 standard deviation (SD)† | ||||||
| • BPI Severity | 0.63 | 0.63 | 0.60 | 0.56 | 0.49 | 0.98 |
| • BPI Interference | 0.84 | 0.91 | 0.77 | 0.74 | 0.67 | 1.05 |
| • BPI Total | 0.70 | 0.74 | 0.63 | 0.63 | 0.56 | 0.98 |
| • PEG | 0.77 | 0.77 | 0.70 | 0.67 | 0.60 | 1.05 |
| 0.50 standard deviation (SD)† | ||||||
| • BPI Severity | 0.90 | .90 | 0.85 | 0.80 | 0.70 | 1.40 |
| • BPI Interference | 1.20 | 1.3 | 1.10 | 1.05 | 0.95 | 1.50 |
| • BPI Total | 1.00 | 1.1 | 0.90 | 0.90 | 0.80 | 1.40 |
| • PEG | 1.10 | 1.1 | 1.00 | 0.95 | 0.85 | 1.50 |
| Variable | SCAMP | INCPAD | SCOPE | CAMEO | SPACE | SSM |
| 1 SEM‡ | ||||||
| • BPI Severity | 0.74 | 0.82 | 0.61 | 0.72 | 0.57 | 1.04 |
| • BPI Interference | 0.87 | 0.86 | 0.76 | 0.77 | 0.75 | 0.74 |
| • BPI Total | 0.69 | 0.70 | 0.54 | 0.63 | 0.58 | 0.69 |
| • PEG | 1.14 | 1.22 | 0.98 | 1.01 | 0.78 | 1.15 |
| 2 SEM‡ | ||||||
| • BPI Severity | 1.48 | 1.65 | 1.23 | 1.44 | 1.13 | 2.08 |
| • BPI Interference | 1.73 | 1.72 | 1.52 | 1.53 | 1.49 | 1.48 |
| • BPI Total | 1.39 | 1.39 | 1.08 | 1.26 | 1.15 | 1.38 |
| • PEG | 2.29 | 2.45 | 1.96 | 2.02 | 1.55 | 2.30 |
Absolute change in score from baseline to follow-up in individuals who reported on the retrospective global anchor that they were “a little better” at follow-up (4 trials). For the SCAMP that used Version A of the retrospective global anchor with 5 categories (rather than 3 categories) of improvement, score changes are for those reporting “a little” or “somewhat” better. Data not available for INCPAD.
Difference of 0.2 SD is often considered a small effect, and 0.5 SD is considered a moderate effect, with 0.35 midway between small and moderate. Some consider 0.35 to 0.50 SD differences as one distribution-based method for estimating minimally important difference (MID)
SEM = standard error of measurement = , where α = Cronbach’s alpha. The SEM is a second distribution-based method of estimating an MID, for which 1 to 2 SEM are often considered the lower and upper bounds.