Asch wanted to test the power of normative social influence on one's likelihood to conform in an unambiguous task. In particular, he wanted to see if there was a unanimous, but incorrect, response, whether the participant would conform.

Asch used a lab experiment to study conformity.  His sample was made up of 123 male students in the USA.  They were told that they were taking part in a ‘vision test’.  In his original study, the independent variable was the "unanimous incorrect response" and the dependent variable was the level of conformity - that is, agreeing with the incorrect response.

In his procedure, he used a naive participant and six confederates. He presented participants with an unambiguous stimulus -­‐ on card 1 there was a single line.  The participants were asked to choose the line on card 2 which was the same length as the first card. There were six confederates who were instructed to give wrong answers on certain trials, and a naive participant who always answered next to last. There were 18 trials - that is, times when they were asked to compare the lines - 12 of which were answered incorrectly by the confederates.

To set up a control for the experiment, Asch had another condition where one participant answered all 18 trials without the confederates present and with only the experimenter in the room. In total, there were 50 "real" participants that took part in the experimental condition and 37 participants in the control condition.

After the experiment was completed, Asch carried out interviews with each of the participants.

Over the 12 critical trials, about 75% of participants conformed at least once, and 25% of participant never conformed. In the control condition, less than 1% of the participants gave the wrong response.

Asch interviewed some of his participants and found that they tended to give one of three reasons for why they conformed: they really thought that they were wrong; they were unsure of their answer; or they didn't want to be ridiculed by the group, so therefore went along with the wrong answer, but knowing that it was incorrect

The task does not have a lot of personal meaning to the participants. Therefore, the task lacks mundane realism and the study lacks ecological validity.

The paradigm has been used repeatedly to test different factors that may influence conformity.

Asch used a control group to make sure that the task was not ambiguous.

There is the ethical concern about the use of deception.

There is a question as to why so few people actually conformed.  Some psychologists have criticized the interpretation of the study as exaggerating the role of group pressure on conformity.

Although interviews after the experiment were used to determine why an individual behaved the way he did, there was no way to actually know what they were thinking and how they made their decisions during the actual experiment. The only way we know is from the participants thinking back and recalling how they made their decisions. 

Although there was sampling bias in the original study, the paradigm has been used with different cultures and genders.