title: Do unblinded assessors bias muscle strength outcomes in randomized controlled trials of progressive resistance strength training in older adults?
abstract: OBJECTIVE
  Knowledge of treatment assignment and failing to analyze results by randomized treatment groups--an intention-to-treat analysis--may cause bias in the treatment effect estimate in randomized controlled trials. This study was undertaken to determine the difference in lower limb muscle strength measured by blinded vs. by unblinded outcome assessors in 73 progressive resistance strength training trials conducted in older adults.
  
  
  METHODS
  Retrospective analysis of randomized controlled trials published before 2007.
  
  
  RESULTS
  Meta-regression analyses showed that trials that used blinded assessors (n = 18) tend to report smaller effect sizes than do those that used unblinded assessors (n = 55), with a difference of -0.80 (95% confidence interval, -1.35 to -0.25). This result still holds even after adjusting for the use of an intention-to-treat analysis, with an adjusted difference of -0.65 (95% confidence interval, -1.26 to -0.04). The reported effects were exaggerated in trials that used unblinded assessors.
  
  
  CONCLUSIONS
  This study suggests that assessor blinding is important and is a safeguard to the internal validity of exercise trials in older adults.
authors.affiliation: Department of Occupational Therapy, School of Health and Rehabilitation Sciences, Indiana University at Indianapolis, 1140 West Michigan Street, Indianapolis, IN 46202-5199, USA.
authors.forename: Chiung-ju
authors.initials: CJ
authors.lastname: Liu
authors.forename: Michael
authors.initials: M
authors.lastname: LaValley
authors.forename: Nancy K
authors.initials: NK
authors.lastname: Latham
mesh_terms: D000368:Aged; D015982:Bias; D004311:Double-Blind Method; D006801:Humans; D035002:Lower Extremity; D008875:Middle Aged; D053580:Muscle Strength; D017063:Outcome Assessment, Health Care; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D012044:Regression Analysis; D055070:Resistance Training; D012189:Retrospective Studies