  User expectations impact the evaluation of new interactive systems. Increased
expectations may enhance the perceived effectiveness of interfaces in user
studies, similar to a placebo effect observed in medical studies. To showcase
the placebo effect, we conducted a user study with 18 participants who
performed a target selection reaction time test with two different display
refresh rates. Participants saw a stated screen refresh rate before every
condition, which corresponded to the true refresh rate only in half of the
conditions and was lower or higher in the other half. Results revealed
successful priming, as participants believed in superior or inferior
performance based on the narrative despite using the opposite refresh rate.
Post-experiment questionnaires confirmed participants still held onto the
initial narrative. Interestingly, the objective performance remained unchanged
between both refresh rates. We discuss how study narratives influence
subjective measures and suggest strategies to mitigate placebo effects in
user-centered study designs.
