Hypothesis awareness as a demand characteristic in laboratory-based eating behaviour research: An experimental study.

Demand characteristics are thought to undermine the validity of psychological research, but the extent to which participant awareness of study hypotheses affects laboratory-measured eating behaviour studies has received limited attention. Participants (N = 84) attended two laboratory sessions in which food intake was measured. In session 1 baseline food intake was measured. In session 2 participants were allocated to either a 'hypothesis aware' or 'hypothesis unaware' condition. Participants were led to believe in the 'hypothesis aware' condition that they were expected to increase their food intake in session 2 relative to session 1. Participants in the 'hypothesis unaware' condition were not provided with hypothesis information. Contrary to our pre-registered predictions, the experimental manipulation of hypothesis awareness did not affect session 2 food intake. However, the manipulation was less effective than anticipated as some participants did not appear to believe the hypothesis information provided. Post-hoc exploratory analyses revealed that participants who believed the study hypothesis was that their food intake would increase in session 2 ate more in session 2 than participants who did not believe this was the study hypothesis. Further confirmatory research is required to understand the causal effect that participant awareness of study hypotheses has on laboratory measured eating behaviour.