The fact that the experimenter remained cool and distant when learner in pain may have led participants to believe it wasn't real
Suggests that there was a lack of realism in Milgram's study = low internal validity
Individual differences
We might find gender differences in obedience, however neither Milgram nor Blass (1999) found differences
Shows that this gender did not impact on obedience levels
Historical validity
Milgram's study was carried out over 50 years ago and the results may not be relevant today
However, Burger (2009) found same levels of obedience as Milgram = suggests results are high in external validity
Milgram's study was considered unethical as there was an apparent lack of concern for the well-being of his participants
Milgram deceived his participants by telling them it was a study on the effects of punishment on learning, and therefore they could not give informed consent
Despite being told at the beginning of the study, the 'prods' from the experimenter made the participants feel like they were unable to withdraw
Milgram's lack of concern for participant well-being undermines scientific credibility