title: Although not consistently superior, the absolute approach to framing the minimally important difference has advantages over the relative approach.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, 1280 Main St West, Hamilton, Ontario, Canada L8S 4K1.
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, 1280 Main St West, Hamilton, Ontario, Canada L8S 4K1.
authors.forename: Shiyuan
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, 1280 Main St West, Hamilton, Ontario, Canada L8S 4K1.
authors.forename: Lehana
authors.initials: L
authors.lastname: Thabane
authors.affiliation: 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.
authors.forename: Toshi A
authors.initials: TA
authors.lastname: Furukawa
authors.affiliation: 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.
authors.forename: Bradley C
authors.initials: BC
authors.lastname: Johnston
authors.affiliation: 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.
authors.forename: Gordon H
authors.initials: GH
authors.lastname: Guyatt
mesh_terms: D004812:Epidemiologic Methods; D006801:Humans; D015201:Meta-Analysis as Topic; D015233:Models, Statistical; D011788:Quality of Life; D012107:Research Design; D011795:Surveys and Questionnaires
keywords: Anchor-based method; Global rating of change; HRQOL; Health-related quality of life; MCID; MID; Minimal important different; PRO; Patient-reported outcomes