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

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. (c) 2008 Elsevier Inc. All rights reserved.