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      Pain relief that matters to patients: systematic review of empirical studies assessing the minimum clinically important difference in acute pain

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          The minimum clinically important difference (MCID) is used to interpret the clinical relevance of results reported by trials and meta-analyses as well as to plan sample sizes in new studies. However, there is a lack of consensus about the size of MCID in acute pain, which is a core symptom affecting patients across many clinical conditions.


          We identified and systematically reviewed empirical studies of MCID in acute pain. We searched PubMed, EMBASE and Cochrane Library, and included prospective studies determining MCID using a patient-reported anchor and a one-dimensional pain scale (e.g. 100 mm visual analogue scale). We summarised results and explored reasons for heterogeneity applying meta-regression, subgroup analyses and individual patient data meta-analyses.


          We included 37 studies (8479 patients). Thirty-five studies used a mean change approach, i.e. MCID was assessed as the mean difference in pain score among patients who reported a minimum degree of improvement, while seven studies used a threshold approach, i.e. MCID was assessed as the threshold in pain reduction associated with the best accuracy (sensitivity and specificity) for identifying improved patients. Meta-analyses found considerable heterogeneity between studies (absolute MCID: I 2 = 93%, relative MCID: I 2 = 75%) and results were therefore presented qualitatively, while analyses focused on exploring reasons for heterogeneity. The reported absolute MCID values ranged widely from 8 to 40 mm (standardised to a 100 mm scale) and the relative MCID values from 13% to 85%. From analyses of individual patient data (seven studies, 918 patients), we found baseline pain strongly associated with absolute, but not relative, MCID as patients with higher baseline pain needed larger pain reduction to perceive relief. Subgroup analyses showed that the definition of improved patients (one or several categories improvement or meaningful change) and the design of studies (single or multiple measurements) also influenced MCID values.


          The MCID in acute pain varied greatly between studies and was influenced by baseline pain, definitions of improved patients and study design. MCID is context-specific and potentially misguiding if determined, applied or interpreted inappropriately. Explicit and conscientious reflections on the choice of a reference value are required when using MCID to classify research results as clinically important or trivial.

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          Most cited references 55

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          Validation of a verbally administered numerical rating scale of acute pain for use in the emergency department.

          Verbally administered numerical rating scales (NRSs) from 0 to 10 are often used to measure pain, but they have not been validated in the emergency department (ED) setting. The authors wished to assess the comparability of the NRS and visual analog scale (VAS) as measures of acute pain, and to identify the minimum clinically significant difference in pain that could be detected on the NRS. This was a prospective cohort study of a convenience sample of adults presenting with acute pain to an urban ED. Patients verbally rated pain intensity as an integer from 0 to 10 (0 = no pain, 10 = worst possible pain), and marked a 10-cm horizontal VAS bounded by these descriptors. VAS and NRS data were obtained at presentation, 30 minutes later, and 60 minutes later. At 30 and 60 minutes, patients were asked whether their pain was "much less," "a little less," "about the same," "a little more," or "much more." Differences between consecutive pairs of measurements on the VAS and NRS obtained at 30-minute intervals were calculated for each of the five categories of pain descriptor. The association between VAS and NRS scores was expressed as a correlation coefficient. The VAS scores were regressed on the NRS scores in order to assess the equivalence of the measures. The mean changes associated with descriptors "a little less" or "a little more" were combined to define the minimum clinically significant difference in pain measured on the VAS and NRS. Of 108 patients entered, 103 provided data at 30 minutes and 86 at 60 minutes. NRS scores were strongly correlated to VAS scores at all time periods (r = 0.94, 95% CI = 0.93 to 0.95). The slope of the regression line was 1.01 (95% CI = 0.97 to 1.06) and the y-intercept was -0.34 (95% CI = -0.67 to -0.01). The minimum clinically significant difference in pain was 1.3 (95% CI = 1.0 to 1.5) on the NRS and 1.4 (95% CI = 1.1 to 1.7) on the VAS. The findings suggest that the verbally administered NRS can be substituted for the VAS in acute pain measurement.
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            Does the clinically significant difference in visual analog scale pain scores vary with gender, age, or cause of pain?

             Ann Kelly (1998)
            To determine the minimum clinically significant difference in visual analog scale (VAS) pain scores for acute pain in the ED setting and to determine whether this difference varies with gender, age, or cause of pain. A prospective, descriptive study of 152 adult patients presenting to the ED with acute pain. At presentation and at 20-minute intervals to a maximum of three measurements, patients marked the level of their pain on a 100-mm, nonhatched VAS. At each follow-up they also gave a verbal rating of their pain as "a lot better," "much the same," "a little worse," or "much worse." The minimum clinically significant difference in VAS pain scores was defined as the mean difference between current and preceding scores when pain was reported as a little worse or a little better. Data were compared based on gender, age more than or less than 50 years, and traumatic vs nontraumatic causes of pain. The minimum clinically significant difference in VAS pain scores is 9 mm (95% CI, 6 to 13 mm). There is no statistically significant difference between the minimum clinically significant differences in VAS pain scores based on gender (p=0.172), age (p=0.782), or cause of pain (p=0.84). The minimum clinically significant difference in VAS pain scores was found to be 9 mm. Differences of less than this amount, even if statistically significant, are unlikely to be of clinical significance. No significant difference in minimum significant VAS scores was found between gender, age, and cause-of-pain groups.
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              Acupuncture treatment for pain: systematic review of randomised clinical trials with acupuncture, placebo acupuncture, and no acupuncture groups

              Objectives To study the analgesic effect of acupuncture and placebo acupuncture and to explore whether the type of the placebo acupuncture is associated with the estimated effect of acupuncture. Design Systematic review and meta-analysis of three armed randomised clinical trials. Data sources Cochrane Library, Medline, Embase, Biological Abstracts, and PsycLIT. Data extraction and analysis Standardised mean differences from each trial were used to estimate the effect of acupuncture and placebo acupuncture. The different types of placebo acupuncture were ranked from 1 to 5 according to assessment of the possibility of a physiological effect, and this ranking was meta-regressed with the effect of acupuncture. Data synthesis Thirteen trials (3025 patients) involving a variety of pain conditions were eligible. The allocation of patients was adequately concealed in eight trials. The clinicians managing the acupuncture and placebo acupuncture treatments were not blinded in any of the trials. One clearly outlying trial (70 patients) was excluded. A small difference was found between acupuncture and placebo acupuncture: standardised mean difference −0.17 (95% confidence interval −0.26 to −0.08), corresponding to 4 mm (2 mm to 6 mm) on a 100 mm visual analogue scale. No statistically significant heterogeneity was present (P=0.10, I2=36%). A moderate difference was found between placebo acupuncture and no acupuncture: standardised mean difference −0.42 (−0.60 to −0.23). However, considerable heterogeneity (P<0.001, I2=66%) was also found, as large trials reported both small and large effects of placebo. No association was detected between the type of placebo acupuncture and the effect of acupuncture (P=0.60). Conclusions A small analgesic effect of acupuncture was found, which seems to lack clinical relevance and cannot be clearly distinguished from bias. Whether needling at acupuncture points, or at any site, reduces pain independently of the psychological impact of the treatment ritual is unclear.

                Author and article information

                BMC Med
                BMC Med
                BMC Medicine
                BioMed Central (London )
                20 February 2017
                20 February 2017
                : 15
                [1 ]Nordic Cochrane Centre, Rigshospitalet, Blegdamsvej 9, Department 7811, 2100 Copenhagen Ø, Denmark
                [2 ]University Hospitals’ Centre for Health Research (UCSF), Rigshospitalet, Blegdamsvej 9, Department 9701, 2100 Copenhagen Ø, Denmark
                [3 ]ISNI 0000 0004 0646 8261, GRID grid.415046.2, , Frederiksberg Hospital, ; Nordre Fasanvej 57, 2000 Frederiksberg, Denmark
                [4 ]ISNI 0000 0001 0674 042X, GRID grid.5254.6, , Section of Biostatistics, University of Copenhagen, ; Østre Farigmagsgade 5, 114 Copenhagen Ø, Denmark
                [5 ]Department of Cardiology, Herlev-Gentofte Hospital, Kildegårdsvej 28, 2900 Hellerup, Denmark
                [6 ]Centre for Evidence-Based Medicine, University of Southern Denmark & Odense University Hospital, Sdr. Boulevard 29, Gate 50 (Videncenteret), 5000 Odense C, Denmark
                © The Author(s). 2017

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                Funded by: Nordic Cochrane Centre
                Research Article
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                © The Author(s) 2017


                pain, minimum clinically important difference, systematic review


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