Standard error of measurement as a valid alternative to minimally important difference for evaluating the magnitude of changes in patient-reported outcomes measures

Abstract

Objective To assess the degree of agreement between standard error of measurement (SEM) and minimally important difference (MID) criteria to evaluate the magnitude of the change caused by a medical intervention. Study Design and Setting Data were obtained from a cohort of 603 patients with neuropathic pain undergoing analgesic treatment with gabapentin who completed four health scales: Medical Outcomes Study Sleep Scale, Sheehan Disability Scale, Covi Anxiety Scale, and Raskin Depression scale. After calculating MID and SEM values for all scales, patients were classified into three categories: improvement, no change, and worsening. Agreement between the two criteria was assessed using Cohen's kappa index of agreement and Kendall's tau-b linear correlation coefficient. Results The 1 SEM criterion showed the highest agreement (kappa = 0.68–1.00) and correlation (tau-b = 0.75–1.00) with the MID criterion. Sensitivity analysis performed in gabapentin responders and nonresponders confirmed the results of the main analysis. Conclusion The 1 SEM criterion is a valid alternative to the MID criterion to evaluate the magnitude of the change produced in patient-reported health outcomes measures.