Yuqing Zhang1, Shiyuan Zhang1, Lehana Thabane1, Toshi A Furukawa2, Bradley C Johnston3, Gordon H Guyatt4. 1. Department of Clinical Epidemiology and Biostatistics, McMaster University, 1280 Main St West, Hamilton, Ontario, Canada L8S 4K1. 2. Departments of Health Promotion and Human Behavior and Clinical Epidemiology, Kyoto University Graduate School of Medicine/School of Public Health, Yoshida Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan. 3. Department of Anaesthesia and Pain Medicine, The Hospital for Sick Children, University of Toronto, 555 University Avenue, Toronto, Ontario, Canada M5G 1X8; Institute of Health Policy, Management and Evaluation, Dalla Lana School of Public Health, University of Toronto, 4th Floor, 155 College St, Toronto, Ontario, Canada M5T 3M6; Child Health Evaluative Sciences, The Hospital for Sick Children Research Institute, 555 University Ave, Toronto, Ontario, Canada M5G 1X8. 4. Department of Clinical Epidemiology and Biostatistics, McMaster University, 1280 Main St West, Hamilton, Ontario, Canada L8S 4K1; Department of Medicine, McMaster University, 1280 Main St West, Hamilton, Ontario, Canada L8S 4K1. Electronic address: guyatt@mcmaster.ca.
Abstract
OBJECTIVES: Using studies that established minimal important difference (MID) using anchor-based methods, we set out to address the relative merits of absolute and relative changes in establishing an instrument's MID. STUDY DESIGN AND SETTING: In seven data sets, we calculated correlations between global change ratings and absolute and relative score changes and conducted meta-analyses. We considered that the measure with the higher correlation represented the more valid approach. RESULTS: The meta-analyses showed no significant difference between pooled correlations of absolute and relative difference on health-related quality of life instrument with global transition scores of symptoms, emotional function, physical function, and cognitive function. In four of five domains, there was at least one study in which the absolute was significantly superior to the relative; in one of these four, one study showed statistically significant superior performance of the relative. In an analysis restricted to patients with low baseline scores for the domain of cognitive function, the relative approach showed higher correlation with global rating than did the absolute approach. CONCLUSION: Although we found no consistent superiority of either approach to establishing the MID, when differences existed they usually favored the absolute, which also has advantages of simplicity and ease of pooling across studies. Researchers may consider the absolute as a default but also compare both methods on an instrument by instrument basis.
OBJECTIVES: Using studies that established minimal important difference (MID) using anchor-based methods, we set out to address the relative merits of absolute and relative changes in establishing an instrument's MID. STUDY DESIGN AND SETTING: In seven data sets, we calculated correlations between global change ratings and absolute and relative score changes and conducted meta-analyses. We considered that the measure with the higher correlation represented the more valid approach. RESULTS: The meta-analyses showed no significant difference between pooled correlations of absolute and relative difference on health-related quality of life instrument with global transition scores of symptoms, emotional function, physical function, and cognitive function. In four of five domains, there was at least one study in which the absolute was significantly superior to the relative; in one of these four, one study showed statistically significant superior performance of the relative. In an analysis restricted to patients with low baseline scores for the domain of cognitive function, the relative approach showed higher correlation with global rating than did the absolute approach. CONCLUSION: Although we found no consistent superiority of either approach to establishing the MID, when differences existed they usually favored the absolute, which also has advantages of simplicity and ease of pooling across studies. Researchers may consider the absolute as a default but also compare both methods on an instrument by instrument basis.
Keywords:
Anchor-based method; Global rating of change; HRQOL; Health-related quality of life; MCID; MID; Minimal important different; PRO; Patient-reported outcomes
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