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’. This study is registered at ClinicalTrials.gov as COB12083. RESULTS Contrary to our hypothesis, raters recorded weights that were 0.293 kilograms heavier when weighing ‘treatment’ versus ‘control’ SPs, though 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 bias which may be created by not blinding research staff who implement weight loss trials as well as the participants in those trials.

Could masking gestational age estimation during scanning improve detection of small-for-gestational-age fetuses? A controlled pre–post evaluation

“…21 Observers may over-or under-estimate seemingly objective measurements, depending on previous information about a research subject. 22 In the context of ultrasound measurements of fetal biometry, operators could be influenced towards a biometry measurement concordant with the known gestational age. An observer-expectancy effect thus would bias measurements towards the normal range for gestational age, which would reduce the likelihood of the detection of SGA.…”