However, due to its extreme unethical nature, replicating this study would not be approved by the BPS. Not only were the participants mentally and physically abused, there was no informed consent as participants did not know what they were signing up for, zimbardo argued this with the concept that deception is necessary to obtain reliable results however for this to be accepted participants need to be informed of their right to withdraw which was not the case with this experiment. Additionally the use of inducement has criticisms in psychological experiments as it discourages participants from withdrawing as they feel since they have been paid they are obligated to continue further increasing the unethicality of this experiment. Another criticism of zimbardos experiment is the high risk of demand characteristics as participants may alter their behaviour based on their interpretation of the purpose of the experiment. For example John Wayne admitted to emphasising his behaviour for the purpose of the experiment, modelling the warden in the movie "cool hand Luke". Furthermore experimenter bias can been seen through zimbardo as he actively involved himself in the experiment as superintendent. This blurred his lines between science and make believe, reducing the research's scientific credibility. Finally, zimbardos experiment had a limited sample size. In order to provide a comprehensive explanation for conformity a more diverse sample was needed e.g. gender, age, and culture to ensure the results can be generalised to society as a whole rather than American male students, for example America is an individualist country (where conformity is less common) so results could differ in collectivist cultures like Asia. Furthermore, volunteer sampling has weaknesses as particular dispositions may be more inclined to volunteer especially since the advertisement of "prison study" can influence the type of participants who volunteer.