demand characteristics

• are extraneous variables within the study where the demands of it make pps behave in ways they would not behave outside of society, reduces a studie's ecological validity
• for example, if a participant guesses the purpose of an experiment they are taking part in, they may try to please the researcher by behaving in the 'right way' rather than the way they naturally would. Alternatively, the pp may rebel against the study and deliberately try to sabotage it (Eg by deliberately giving wrong answers)