Introducing the Concept of the Minimally Important Difference to Determine a Clinically Relevant Change on Patient-Reported Outcome Measures in Patients with Intermittent Claudication

Abstract

PurposeThe minimally important difference (MID) represents the smallest change in score on patient-reported outcome measures that is relevant to patients. The aim of this study was to introduce the MID for the Vascular Quality of Life Questionnaire (VascuQol) and the walking impairment questionnaire (WIQ) for patients with intermittent claudication (IC).MethodsIn this multicenter study, we recruited 294 patients with IC between July and October 2012. Patients completed the VascuQol, with scores ranging from 1 to 7 (worst to best), and the WIQ, with scores ranging from 0 to 1 (worst to best) at first visit and after 4 months follow-up. In addition, patients answered an anchor-question rating their health status compared to baseline, as being improved, unchanged, or deteriorated. The MID for improvement and deterioration was calculated by an anchor-based approach, and determined with the upper and lower limits of the 95 % confidence interval of the mean change of the group who had not changed according to the anchor-question.ResultsFor the MID analyses of the VascuQol and WIQ, 163 and 134 patients were included, respectively. The MID values for the VascuQol (mean baseline score 4.25) were 0.87 for improvement and 0.23 for deterioration. For the WIQ (mean baseline score 0.39), we found MID values of 0.11 and −0.03 for improvement and deterioration, respectively.ConclusionIn this study, we calculated the MID for the VascuQol and the WIQ. Applying these MID facilitates better interpretation of treatment outcomes and can help to set treatment goals for individual care.Electronic supplementary materialThe online version of this article (doi:10.1007/s00270-015-1060-0) contains supplementary material, which is available to authorized users.

Determining the Minimally Important Difference for the VascuQol Sumscore and Its Domains in Patients with Intermittent Claudication

“…1 The values in the current study also greatly exceed the MID value of .87 for the VascuQol sumscore from our previous study. 6 The follow up period in that study was only 4 months and exercise programs of SET patients were still ongoing. These patients might therefore not have reached the maximum increase in VascuQol scores at the time of the second measurement.…”

“…Two previously reported anchor based methods were used to calculate the MID. 6,14 With the 95% confidence interval (CI) method the MID was expressed as the upper and lower limit of the 95% CI of the change in score of the group who considered themselves unchanged according to the GRC question and the HTI. The CI for continuous variables can be calculated as the sample mean AE t (SD/On) where the t value is based on the degrees of freedom (n e 1) and n is the number of observations.…”

“…5 In a previous study, the concept of MID was applied in patients with IC and was calculated for improvement and deterioration on the VascuQol sumscore. 6 As only one general anchor question was included, it was not possible to calculate MID values for the different domain scores of the VascuQol. However, the five domains of the VascuQol measure distinctly different aspects of quality of life (QOL).…”

Test–retest Reliability and Measurement Error Are Excellent for the Dutch Version of the VascuQol Questionnaire in Patients with Intermittent Claudication

“…The second, recently published study determined the MID in a larger cohort of claudicants and found an MID of 0.87 to show a clinically relevant improvement. 11 The fact that the SEM of 0.34 found for the VascuQol sumscore is indeed smaller than the aforementioned MID values indicates that clinically relevant changes over time can be detected, for example, in longitudinal studies or clinical practice.…”

Minimally Important Difference of the Absolute and Functional Claudication Distance in Patients with Intermittent Claudication

“…7 It was first described by Jaeschke et al 8 in an attempt to elucidate what change in an asthma QoL questionnaire score would be meaningful. Recently, Conijn et al 9 introduced the MID for an IC population. In their study, the MID was calculated for the Walking Impairment Questionnaire (WIQ); a patient reported assessment of walking impairment.…”