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Allison, Dutton, and Fontaine lead team investigating influence of researchers’ expectations on accuracy of weight loss trial data

January 7, 2015



Researchers and participants' expectations can influence treatment response. Less is known about the effects of researchers' expectations on the accuracy of data collection in a weight loss trial. Therefore, David B. Allison, PhD, distinguished professor and director of the Nutrition Obesity Research Center (NORC) and Office of Energetics, Gareth R. Dutton, PhD, associate professor in the Division of Preventive Medicine, and Kevin R. Fontaine, PhD, professor and chair in the Department of Health Behavior—in collaboration with Office of Energetics postdoctoral scholars John Dawson, PhD, and Patrice L. Capers, PhD—recruited 58 student raters with an average age of 20.1 years to weigh individuals whom the student raters thought were completing a 12-month weight loss trial but who were, in actuality,  standardized patients (SPs) playing these roles.

Prior to data collection, student raters were provided information suggesting that the tested weight loss treatment had been effective. Each student rater received a list of 9 or 10 “participants” to weigh. While the list identified each person as “treatment” or “control,” this assignment was at random, which allowed the researchers to examine the effects of non-blinding and expectancy manipulation on weight measurement accuracy. They hypothesized that raters would record the weights of “treatment participants” as lower than those of “control participants.” However, contrary to this hypothesis, raters actually recorded weights that were 0.293 kilograms heavier when weighing treatment versus control SPs, although the difference was not statistically significant.

The pilot study found no evidence that manipulating expectancies about treatment efficacy or not blinding raters biased measurements. The team concluded that future work should examine other biases that may be created by not blinding research staff who implement weight loss trials, as well as the participants in those trials.

To read “Randomized Controlled Trial Examining Expectancy Effects on the Accuracy of Weight Management,” published in December 2014 in the journal Clinical Obesity, click here.