How to analyze the Visual Analogue Scale: Myths, truths and clinical relevance

Abstract

<jats:title>Abstract</jats:title><jats:sec id="j_j.sjpain.2016.06.012_s_005_w2aab2b8c73b1b7b1aab1c16b1Aa"><jats:title>Background and aims</jats:title><jats:p>The Visual Analogue Scale (VAS) is a popular tool for the measurement of pain. A variety of statistical methods are employed for its analysis as an outcome measure, not all of them optimal or appropriate. An issue which has attracted much discussion in the literature is whether VAS is at a ratio or ordinal level of measurement. This decision has an influence on the appropriate method of analysis. The aim of this article is to provide an overview of current practice in the analysis of VAS scores, to propose a method of analysis which avoids the shortcomings of more traditional approaches, and to provide best practice recommendations for the analysis of VAS scores.</jats:p></jats:sec><jats:sec id="j_j.sjpain.2016.06.012_s_006_w2aab2b8c73b1b7b1aab1c16b2Aa"><jats:title>Methods</jats:title><jats:p>We report on the current usage of statistical methods, which fall broadly into two categories: those that assume a probability distribution for VAS, and those that do not. We give an overview of these methods, and propose continuous ordinal regression, an extension of current ordinal regression methodology, which is appropriate for VAS at an ordinal level of measurement. We demonstrate the analysis of a published data set using a variety of methods, and use simulation to compare the power of the various methods to detect treatment differences, in differing pain situations.</jats:p></jats:sec><jats:sec id="j_j.sjpain.2016.06.012_s_007_w2aab2b8c73b1b7b1aab1c16b3Aa"><jats:title>Results</jats:title><jats:p>We demonstrate that continuous ordinal regression provides the most powerful statistical analysis under a variety of conditions.</jats:p></jats:sec><jats:sec id="j_j.sjpain.2016.06.012_s_008_w2aab2b8c73b1b7b1aab1c16b4Aa"><jats:title>Conclusions and Implications</jats:title><jats:p> We recommend that in the situation in which no covariates besides treatment group are included in the analysis, distribution-free methods (Wilcoxon, Mann–Whitney) be used, as their power is indistinguishable from that of the proposed method. In the situation in which there are covariates which affect VAS, the proposed method is optimal. However, in this case, if the VAS scores are not concentrated around either extreme of the scale, normal-distribution methods (<jats:italic>t</jats:italic>-test, linear regression) are almost as powerful, and are recommended as a pragmatic choice. In the case of small sample size and VAS skewed to either extreme of the scale, the proposed method has vastly superior power to other methods.</jats:p></jats:sec>

The effectiveness of hydrodistension and physiotherapy following previously failed conservative management of frozen shoulder in a UK primary care centre

“…As such, these data are presented as the median and interquartile range ( Figure 1) and were rank-transformed prior to analysis. We assessed changes in pain from pre-hydrodistension using the Wilcoxon test, as recommended for such data (Heller, Manuguerra, & Chow, 2016 Uncertainty in all estimates were expressed as 90% confidence intervals (CIs). We subsequently applied a calibrated Bayesian approach with a least-informative prior (i.e., clinical magnitude-based decisions) (Batterham & Hopkins, 2006;Hopkins & Batterham, 2019) to describe the size and precision of these changes.…”

“…As such, these data are presented as the median and interquartile range (Figure ) and were rank‐transformed prior to analysis. We assessed changes in pain from pre‐hydrodistension using the Wilcoxon test, as recommended for such data (Heller, Manuguerra, & Chow, ). These analyses were performed in R (version 3.4.1, R Foundation for Statistical Computing, Vienna, Austria).…”

Widening the search for suspect data – is the flood of retractions about to become a tsunami?

“…Selecting outcomes on which to measure reductions in pain is also controversial. Debate exists on the use of traditional methods such as visual analogue scales and whether these are treated as ratio or ordinal data [14]. Therefore, some researchers in the field advocate similar measures to those used in this study, such as no worse than mild pain [13].…”

Patient controlled analgesia: effective and cost‐effective management of acute pain within the Emergency Department?

“…Selecting outcomes on which to measure reductions in pain is also controversial. Debate exists on the use of traditional methods such as visual analogue scales and whether these are treated as ratio or ordinal data . Therefore, some researchers in the field advocate similar measures to those used in this study, such as no worse than mild pain .…”