Demand characteristics

In research—particularly psychology—demand characteristics refers to an experimental artifact where participants form an interpretation of the experiment's purpose and subconsciously change their behavior to fit that interpretation. Pioneering research was conducted on demand characteristics by Martin Orne. Typically, they are considered an extraneous variable, exerting an effect on behavior other than that intended by the experimenter.

A possible reason for demand characteristics is the participant's expectation that he or she will somehow be evaluated and thus figures out a way to 'beat' the experiment to attain good scores in the alleged evaluation. Demand characteristics cannot be eliminated from experiments, but demand characteristics can be studied to see their effect on the experiment. Examples of some common demand characteristics:

Weber and Cook have described some demand characteristics as involving the participant taking on a role in the experiment. These roles include:

Researchers use a number of different approaches for dealing with demand characteristics in research situations. Some of the more common approaches include the following:

...
Wikipedia