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Randomized controlled trial examining expectancy effects on the accuracy of weight measurement
Author(s) -
Dutton G. R.,
Fontaine K. R.,
Alcorn A. S.,
Dawson J.,
Capers P. L.,
Allison D. B.
Publication year - 2015
Publication title -
clinical obesity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.64
H-Index - 12
eISSN - 1758-8111
pISSN - 1758-8103
DOI - 10.1111/cob.12083
Subject(s) - blinding , medicine , expectancy theory , context (archaeology) , randomized controlled trial , data collection , weight control , clinical psychology , psychology , social psychology , statistics , obesity , paleontology , mathematics , biology
Summary 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.