Rescaling pain intensity measures for meta-analyses of analgesic medicines for low back pain appears justified: an empirical examination from randomised trials

Abstract

Objective Meta-analyses of analgesic medicines for low back pain often rescale measures of pain intensity to use mean difference (MD) instead of standardised mean difference for pooled estimates. Although this improves clinical interpretability, it is not clear whether this method is justified. Our study evaluated the justification for this method. Methods We identified randomised clinical trials of analgesic medicines for adults with low back pain that used two scales with different ranges to measure the same construct of pain intensity. We transformed all data to a 0–100 scale, then compared between-group estimates across pairs of scales with different ranges. Results Twelve trials were included. Overall, differences in means between pain intensity measures that were rescaled to a common 0–100 scale appeared to be small and randomly distributed. For one study that measured pain intensity on a 0–100 scale and a 0–10 scale; when rescaled to 0–100, the difference in MD between the scales was 0.8 points out of 100. For three studies that measured pain intensity on a 0–10 scale and 0–3 scale; when rescaled to 0–100, the average difference in MD between the scales was 0.2 points out of 100 (range 5.5 points lower to 2.7 points higher). For two studies that measured pain intensity on a 0–100 scale and a 0–3 scale; when rescaled to 0–100, the average difference in MD between the scales was 0.7 points out of 100 (range 6.2 points lower to 12.1 points higher). Finally, for six studies that measured pain intensity on a 0–100 scale and a 0–4 scale; when rescaled to 0–100, the average difference in MD between the scales was 0.7 points (range 5.4 points lower to 8.3 points higher). Conclusion Rescaling pain intensity measures may be justified in meta-analyses of analgesic medicines for low back pain. Systematic reviewers may consider this method to improve clinical interpretability and enable more data to be included. Study registration/data availability Open Science Framework (osf.io/8rq7f).

Comparative effectiveness and safety of analgesic medicines for adults with acute non-specific low back pain: systematic review and network meta-analysis

“…Data from studies that reported multiple measures for function were prioritised similarly: Oswestry Disability Index,42 Roland Morris Disability Questionnaire,43 rating scale from a composite measure, ordinal scale 1736. Data for pain intensity and function were normalised to 0-100 scales before analysis to improve clinical interpretability 91044. Data presented in other forms (eg, median or standard error) were transformed 4546.…”

The level of agreement between the numerical rating scale and visual analogue scale for assessing pain intensity in adults with chronic pain

“…The rationale for this approach relies on the correlation between the different pain intensity scores. This approach to rescale pain intensity measures to a 0-100 scale in the context of meta-analyses was formally tested by Wewege et al [41]. One study measured pain intensity on a 0-100 scale and a 0-10 scale; when the latter was rescaled to 0-100, the difference in mean difference between the scales was 0.8 points out of 100 and the study weight demonstrated a difference of 10% [41].…”

“…This approach to rescale pain intensity measures to a 0-100 scale in the context of meta-analyses was formally tested by Wewege et al [41]. One study measured pain intensity on a 0-100 scale and a 0-10 scale; when the latter was rescaled to 0-100, the difference in mean difference between the scales was 0.8 points out of 100 and the study weight demonstrated a difference of 10% [41]. This result indicated that rescaling pain intensity measures to a common scale may be appropriate for meta-analyses, but the authors stressed that results may not be generalisable outside the setting of analgesic medicines for lower back pain [41].…”

“…One study measured pain intensity on a 0–100 scale and a 0–10 scale; when the latter was rescaled to 0–100, the difference in mean difference between the scales was 0.8 points out of 100 and the study weight demonstrated a difference of 10% [41]. This result indicated that rescaling pain intensity measures to a common scale may be appropriate for meta‐analyses, but the authors stressed that results may not be generalisable outside the setting of analgesic medicines for lower back pain [41]. Combining these results indicates that although there are differences between both pain intensity scales (as shown in the current study), rescaling pain intensity scores to another scale may be justified in the context of a meta‐analysis; however, further research is needed to confirm this hypothesis.…”

The Efficacy of Graded Motor Imagery and Its Components on Phantom Limb Pain and Disability: A Systematic Review and Meta-Analysis

“… 31 We converted the scores of the two studies 6 , 32 that assessed pain using a 0 to 10 scale to a 0 to 100 scale by multiplying the mean and standard deviation with the range of the new scale. 33 Funnel plots were generated to assess for possible publication bias whenever possible. We assessed statistical heterogeneity using the I 2 statistic and rated the level of heterogeneity as low (0%–25%), moderate (>25%–50%), or high (>50%).…”