Determining the Michigan Hand Outcomes Questionnaire Minimal Clinically Important Difference by Means of Three Methods :

This study used the standard error of measurement (SEM) to evaluate intra-individual change on both the Chronic Respiratory Disease Questionnaire (CRQ) and the SF-36. After analyzing the reliability and validity of both instruments at baseline among 471 COPD outpatients, the SEM was compared to established minimal clinically important difference (MCID) standards for three CRQ dimensions. A value of one SEM closely approximated the MCID standards for all CRQ dimensions. This SEM-based criterion was then validated by cross-classifying the change status (improved, stable, or declined) of 393 follow-up outpatients using the one-SEM criterion and the MCID standard. Excellent agreement was achieved for all three CRQ dimensions. Although MCID standards have not been established for the SF-36, the one-SEM criterion was explored in these change scores. Among SF-36 scales demonstrating acceptable reliability and reasonable variance, the percent of individuals within each change category was consistent with those seen in the CRQ dimensions. These results replicate previous findings where a value of one SEM also closely approximated MCIDs for all dimensions of the Chronic Heart Disease Questionnaire among cardiovascular outpatients. The one-SEM criterion should be explored in other health-related quality of life instruments with established MCIDs.

Changes in scores on health status questionnaires are difficult to interpret. Several methods to determine minimally important changes (MICs) have been proposed which can broadly be divided in distribution-based and anchor-based methods. Comparisons of these methods have led to insight into essential differences between these approaches. Some authors have tried to come to a uniform measure for the MIC, such as 0.5 standard deviation and the value of one standard error of measurement (SEM). Others have emphasized the diversity of MIC values, depending on the type of anchor, the definition of minimal importance on the anchor, and characteristics of the disease under study. A closer look makes clear that some distribution-based methods have been merely focused on minimally detectable changes. For assessing minimally important changes, anchor-based methods are preferred, as they include a definition of what is minimally important. Acknowledging the distinction between minimally detectable and minimally important changes is useful, not only to avoid confusion among MIC methods, but also to gain information on two important benchmarks on the scale of a health status measurement instrument. Appreciating the distinction, it becomes possible to judge whether the minimally detectable change of a measurement instrument is sufficiently small to detect minimally important changes.

In this study, psychometric principles were used to develop an outcomes questionnaire capable of measuring health state domains important to patients with hand disorders. These domains were hypothesized to include (1) overall hand function, (2) activities of daily living (ADL), (3) pain, (4) work performance, (5) aesthetics, and (6) patient satisfaction with hand function. An initial pool of 100 questions was pilot-tested for clarity in 20 patients; following factor analysis, the number of questions was reduced to a 37-item Michigan Hand Outcomes Questionnaire (MHQ). The MHQ, along with the Short Form-12, a generic health status outcomes questionnaire, was then administered to 200 consecutive patients at a university-based hand surgery clinic and was subjected to reliability and validity testing. The mean time required to complete the questionnaire was 10 minutes (range, 7-20 minutes). Factor analysis supported the 6 hypothesized scales. Test-retest reliability using Spearman's correlation demonstrated substantial agreement, ranging from 0.81 for the aesthetics scale to 0.97 for the ADL scale. In testing for internal consistency, Cronbach's alphas ranged from 0.86 for the pain scale to 0.97 for the ADL scale (values >0.7 for Cronbach's alpha are considered a good internal consistency). Correlation between scales gave evidence of construct validity. In comparing similar scales in the MHQ and the Short Form-12, a moderate correlation (range, 0.54-0.79) for the ADL, work performance, and pain scales was found. In evaluating the discriminate validity of the aesthetics scale, a significant difference (p = .0012) was found between the aesthetics scores for patients with carpal tunnel syndrome and patients with rheumatoid arthritis. The MHQ is a reliable and valid instrument for measuring hand outcomes. It can be used in a clinic setting with minimal burden to patients. The questions in the MHQ have undergone rigorous psychometric testing, and the MHQ is a promising instrument for evaluation of outcomes following hand surgery.