title: Combining follow-up and change data is valid in meta-analyses of continuous outcomes: a meta-epidemiological study.
abstract: OBJECTIVE
  To investigate whether it is valid to combine follow-up and change data when conducting meta-analyses of continuous outcomes.
  
  
  METHODS
  Meta-epidemiological study of randomized controlled trials in patients with osteoarthritis of the knee/hip, which assessed patient-reported pain. We calculated standardized mean differences (SMDs) based on follow-up and change data, and pooled within-trial differences in SMDs. We also derived pooled SMDs indicating the largest treatment effect within a trial (optimistic selection of SMDs) and derived pooled SMDs from the estimate indicating the smallest treatment effect within a trial (pessimistic selection of SMDs).
  
  
  RESULTS
  A total of 21 meta-analyses with 189 trials with 292 randomized comparisons in 41,256 patients were included. On average, SMDs were 0.04 standard deviation units more beneficial when follow-up values were used (difference in SMDs: -0.04; 95% confidence interval: -0.13, 0.06; P=0.44). In 13 meta-analyses (62%), there was a relevant difference in clinical and/or significance level between optimistic and pessimistic pooled SMDs.
  
  
  CONCLUSIONS
  On average, there is no relevant difference between follow-up and change data SMDs, and combining these estimates in meta-analysis is generally valid. Decision on which type of data to use when both follow-up and change data are available should be prespecified in the meta-analysis protocol.
authors.affiliation: Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland.
authors.forename: Bruno R
authors.initials: BR
authors.lastname: da Costa
authors.forename: Eveline
authors.initials: E
authors.lastname: Nüesch
authors.forename: Anne W
authors.initials: AW
authors.lastname: Rutjes
authors.forename: Bradley C
authors.initials: BC
authors.lastname: Johnston
authors.forename: Stephan
authors.initials: S
authors.lastname: Reichenbach
authors.forename: Sven
authors.initials: S
authors.lastname: Trelle
authors.forename: Gordon H
authors.initials: GH
authors.lastname: Guyatt
authors.forename: Peter
authors.initials: P
authors.lastname: Jüni
mesh_terms: D016021:Epidemiologic Studies; D006801:Humans; D015201:Meta-Analysis as Topic; D010003:Osteoarthritis; D017063:Outcome Assessment, Health Care / Q000706:statistics & numerical data*; D010147:Pain Measurement / Q000706:statistics & numerical data; D016032:Randomized Controlled Trials as Topic; D013223:Statistics as Topic / Q000379:methods*