Demand Characteristics is a term used in Cognitive Psychology to denote the situation where the results of an experiment are biased because the experimenters' expectancies regarding the performance of the participants on a particular task create an implicit demand for the participants to perform as expected. Margarat Intons-Peterson (1983) has investigated demand characteristics through experiments in which she manipulated with her participants' performance by 'leaking' what she expected the results would be like. If participants in the experiment knew that Margarat Intons-Peterson expected their performance on task A to be better than that of task B, their actual performance on task A would in fact be comparatively better (measured relative to a control group of participants who performed task A not knowing about the expectancies).
16.0.1 Relevance for interaction design
People apparently have a tendency to conform to known expectancies and are good at picking up the designer's intentions, expectations, and opinions. Even subtle and implicit cues like body language, wording of a phrase etc is enough to make your expectancies known to the user. Therefore, any user events (prototyping sessions, workshops etc.) should be carefully planed with regards to how the users are informed about the event. If, for example, they are given three competing prototypes and they somehow pick up your expectancies (maybe one prototype looks more 'finished' than the others), it will influence the results. Keeping demand characteristics in mind will help a designer avoid its resulting methodological problems.