title: Meta-analysis on continuous outcomes in minimal important difference units: an application with appropriate variance calculations.
abstract: To compare results from meta-analyses for mean differences in minimal important difference (MID) units (MDMID), when MID is treated as a random variable vs. a constant.
  
  
  
  Meta-analyses of published data. We calculated the variance of MDMIDas a random variable using the delta method and as a constant. We assessed performance under different assumptions. We compare meta-analysis results from data originally used to present the MDMIDand data from osteoarthritis studies using different domain instruments.
  
  
  
  Depending on the data set and depending on the values of rho and coefficient of variation of the MID (CoVMID), estimates of treatment effect and P-values between an approach considering the MID as a constant vs. as a random variable may differ appreciably. Using our data sets, we provide examples of the potential magnitude. When rho = 0.5 and CoVMID= 0.8, considering MID as a constant overestimated the treatment effect by 33-110% and decreased the P-value for heterogeneity from above 0.95 to below 0.08. When rho = 0.8 and CoVMID= 0.5, the magnitude of the effects was similar.
  
  
  
  Considering MID as a random variable avoids unrealistic assumptions and provides more appropriate treatment effect estimates.
authors.affiliation: Centre for Clinical Epidemiology, Lady Davis Institute, Jewish General Hospital, McGill University, 3755 Cote Ste-Catherine Road, Montreal, Quebec H3T 1E2, Canada. Electronic address: ian.shrier@mcgill.ca.
authors.forename: Ian
authors.initials: I
authors.lastname: Shrier
authors.affiliation: The Parker Institute, Bispebjerg and Frederiksberg Hospital, Nordre Fasanvej 57, DK-2000 Copenhagen F, Denmark.
authors.forename: Robin
authors.initials: R
authors.lastname: Christensen
authors.affiliation: Research Unit for Musculoskeletal Function and Physiotherapy, Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark; Department of Physiotherapy and Occupational Therapy, Copenhagen University Hospital, Herlev and Gentofte, Kildegaardsvej 28, 2900 Hellerup, Copenhagen, Denmark.
authors.forename: Carsten
authors.initials: C
authors.lastname: Juhl
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, Faculty of Health Sciences, McMaster University, 1280 Main Street West, MDCL 3211, Hamilton, ON L8S 4K1, Canada; Department of Mathematics & Statistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada.
authors.forename: Joseph
authors.initials: J
authors.lastname: Beyene
mesh_terms: D003627:Data Interpretation, Statistical; D016021:Epidemiologic Studies; D006801:Humans; D015201:Meta-Analysis as Topic
keywords: Continuous outcomes; Meta-analysis; Methods; Minimal important difference; Ratio of means; Standardized mean difference; Variance