Abstract
Background
The minimum clinically important difference (MCID) is used to interpret the relevance
of treatment effects, e.g., when developing clinical guidelines, evaluating trial
results or planning sample sizes. There is currently no agreement on an appropriate
MCID in chronic pain and little is known about which contextual factors cause variation.
Methods
This is a systematic review. We searched PubMed, EMBASE, and Cochrane Library. Eligible
studies determined MCID for chronic pain based on a one-dimensional pain scale, a
patient-reported transition scale of perceived improvement, and either a mean change
analysis (mean difference in pain among minimally improved patients) or a threshold
analysis (pain reduction associated with best sensitivity and specificity for identifying
minimally improved patients). Main results were descriptively summarized due to considerable
heterogeneity, which were quantified using meta-analyses and explored using subgroup
analyses and metaregression.
Results
We included 66 studies (31.254 patients). Median absolute MCID was 23 mm on a 0–100 mm
scale (interquartile range [IQR] 12–39) and median relative MCID was 34% (IQR 22–45)
among studies using the mean change approach. In both cases, heterogeneity was very
high: absolute MCID I2 = 99% and relative MCID I2 = 96%. High variation was also seen among studies using the threshold approach: median
absolute MCID was 20 mm (IQR 15–30) and relative MCID was 32% (IQR 15–41). Absolute
MCID was strongly associated with baseline pain, explaining approximately two-thirds
of the variation, and to a lesser degree with the operational definition of minimum
pain relief and clinical condition. A total of 15 clinical and methodological factors
were assessed as possible causes for variation in MCID.
Conclusions
MCID for chronic pain relief vary considerably. Baseline pain is strongly associated
with absolute, but not relative, measures. To a much lesser degree, MCID is also influenced
by the operational definition of relevant pain relief and possibly by clinical condition.
Explicit and conscientious reflections on the choice of an MCID are required when
classifying effect sizes as clinically important or trivial.
Keywords
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Article info
Publication history
Published online: May 21, 2018
Accepted:
May 14,
2018
Footnotes
Funding: The study was funded by the Nordic Cochrane Center.
Ethics approval and consent to participate: No ethics committee approval was needed for this systematic review.
Availability of data and material: The data set analyzed during the present study is available from the corresponding author on request. The review protocol has been submitted to Journal of Clinical Epidemiology and can be obtained from the corresponding author on request.
Conflict of interests: The authors declare that they have no conflict of interests.
Authors' contributions: A.H., B.T., and M.F.O. conceptualized the study. M.F.O., E.B., M.D.H., and B.T. contributed to the acquisition of data. Data was analyzed by M.F.O. with the assistance of J.H. M.F.O., J.H., and A.H. contributed to the interpretation of results. M.F.O. and A.H. drafted the article, all coauthors contributed to reviewing the article.
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