title: Randomized controlled trial examining expectancy effects on the accuracy of weight measurement.
abstract: BACKGROUND
  Researchers and participants' expectations can influence treatment response. Less is known about the effects of researchers' expectations on the accuracy of data collection in the context of a weight loss trial.
  
  
  METHODS
  Student raters (N = 58; age = 20.1 ± 2.3 years) were recruited to weigh individuals who they thought were completing a 12-month weight loss trial, although these 'participants' were actually standardized patients (SPs) playing these roles. Prior to data collection, student raters were provided information suggesting that the tested treatment had been effective. Each student rater received a list of 9-10 'participants' to weigh. While the list identified each person as 'treatment' or 'control', this assignment was at random, which allowed us to examine the effects of non-blinding and expectancy manipulation on weight measurement accuracy. We hypothesized that raters would record the weights of 'treatment participants' as lower than those of 'control participants'.
  
  
  RESULTS
  Contrary to our hypothesis, raters recorded weights that were 0.293 kg heavier when weighing 'treatment' vs. 'control' SPs, although this difference was not significant (P = 0.175).
  
  
  CONCLUSIONS
  This pilot study found no evidence that manipulating expectancies about treatment efficacy or not blinding raters biased measurements. Future work should examine other biases which may be created by not blinding research staff who implement weight loss trials as well as the participants in those trials.
authors.affiliation: University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: G R
authors.initials: GR
authors.lastname: Dutton
authors.forename: K R
authors.initials: KR
authors.lastname: Fontaine
authors.forename: A S
authors.initials: AS
authors.lastname: Alcorn
authors.forename: J
authors.initials: J
authors.lastname: Dawson
authors.forename: P L
authors.initials: PL
authors.lastname: Capers
authors.forename: D B
authors.initials: DB
authors.lastname: Allison
mesh_terms: D003625:Data Collection / Q000379:methods*; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D010865:Pilot Projects; D015203:Reproducibility of Results; D035842:Research Subjects; D015983:Selection Bias; D015431:Weight Loss; D061217:Weight Reduction Programs
keywords: Expectancy effect; measurement; randomized controlled trial; weight