One weakness of the Milgram (1963) study was that there was a lack of opportunity for participants to withdraw from the experiment. This is significant because while taking part in the experiment a number of participants expressed they were uncomfortable but were denied the opportunity to withdraw. This may make participants feel 'trapped' in that they are forced to inflict pain on another, even though they are against doing so in that situation.
Milgram's (1963) experiment has many pros and cons, one of the cons of his experiment is that tje samlle of subjects was 40 male Americans. This is significant because the results will not represent the obedience rates of both genders, decreasing ecological validity. Furthermore, with only American participants being selected, cultural factors may have played a cruicial part in the obedience rates found. This means the results may not represent wider obedience rates across the world, in different cultures, further decresding the ecological validity.