According to Leon Mann, conformity means "yielding to group pressures". Everyone is a member of one group oranother and everyone expects members of these groups to behave in certain ways. If you are a member of an identifiable group you are expected to behave appropriately to it. If you don"t confirm and behave appropriately you are likely to be rejected by the group.
Like stereotypes, conforming and expecting others to conform maintains cognitive balance.

There are several kinds of conformity. Many studies of conformity took place in the 1950"s which led Kelman to distinguish between compliance, internalisation and identification. Compliance is the type of conformity where the subject goes along with the group view, but privately disagrees with it. Internalisation is where the subject comes to accept, and eventually believes in the group view.
Identification is where the subject accepts and believes the group view, because he or she wants to become associated with the group.

Leon Mann identifies normative conformity which occurs when direct group pressure forces the individual to yield under the threat of rejection or the promise of reward. This can occur only if someone wants to be a member of the group or the groups attitudes or behaviour are important to the individual in some way.

Apart from normative conformity there is informational conformity which occurs where the situation is vague or ambiguous and because the person is uncertain he or she turns to others for evidence of the appropriate response.

Thirdly, Mann identifies ingratiational conformity which occurs where a person tries to do whatever he or she thinks the others will approve in order to gain acceptance
(if you make yourself appear to be similar to someone else, they might come to like you).

The first major research into conformity was conducted in
1935 by Sherif who used a visual illusion, known as the auto-kinetic effect. Sherif told his subjects that a spot of light which they were about to see in a darkened room was going to move, and he wanted them to say the direction and distance of the movement. In the first experimental condition the subjects were tested individually. Some said the distance of movement wasn"t very far in any directio, others said it was several inches. Sherif recorded each subjects response. In the second experimental condition,
Sherif gathered his subjects into groups, usually of three people, and asked them to discribe verbally the movement of light. He gave them no instructions as to whether they needed to reach any kind of agreement among themselves but simply asked them to give their own reports while being aware of the reports that other members gave. During the group sessions it became apparent that the subjects reports strarted to converge much nearer to an average of what their individual reports had been. If a subject who had said that the light didn"t move very far when tested individually said "I think it is moving 2 inches to the left" then another who had reported movement of 4 inches, when tested individually, might say "I think it may have been 3 inches".
As the number of reported movements continued the more the members of the group conformed to each others reports. This spot of light was in fact stationary so whatever reports were made was the consequence of the subject imagining they saw something happen. So they were not certain about the movement they observed and so would not feel confident about insisting that their observations were wholly correct. When they heard other reported judgements they may have decided to go along with them.

The problem with this study, for understanding of conformity, as one aspect of social psychology is that it is a total artifical experimental situation - there isn"t even a right answer. Requested reports of imaginary movements of a stationary spot of light in a darkened room when alone, or with two others, hardly reflects situations we come accross in our every day lives. Generalising from its conclusions to real life might be innacurate. However, some of them do have a common sense appeal.

Ash was a harsh critic of Sherifs experimental design and claimed that it showed little about conformity since there was no right answer to conform to. Ash designed an experiment where there could be absolutely no doubt about whether subjects would be conforming or not and it was absolutely clear what they were conforming to. He wanted to be able to put an individual under various amounts of group pressure that he could control and manipulate and measure their willingness to conform to the groups response to something that was clearly wrong. Ash conducted what are now described as classic experiments in conformity. This is not to say they aren"t criticised today or that its conclusions are wholly acceptable now - they showed the application of the scientific method to social psychology and we used as models of how to conduct psychological research.

In an early experiment Ash gathered a group of seven university students in a classroom. They sat around one side of a large table facing the blackboard. On the left side of the board there was a white card with a single black line drawn vertically on it. On the right of the board there was another white card with three vertical lines of different lengths. Two of the lines on the card on the right were longer or shorther than the target line. Matching the target line to the comparison line shouldn"t have been a difficult task however for these seven students, all but one was a confederate of Ash and they had been instructed to give incorrect responses on seven of the twelve trials. The one naive subject was seated either at the extreme left or next to the extreme left of the line of students so that he would always be last (or next to last) to answer. He would have heard most of the others give their judgements about which comparison line matches the target line before he spoke.
The naive subject was a member of a group he didn"t know and might never see again who suddenly and for no apparent reason started saying something which directly contradicted the evidence of his own eyes.

In subsequent experiments Ash used between 7 and 9 subjects using the same experimental procedure. In the first series of experiments he tested 123 naives on 12 critical tests where 7 were going to be incorrect. Each naive therefore had 7 opportunities to conform to something they could see to be wrong. One third of the naives conformed on all 7 occasions. About three quarters of them conformed on at least one occasion. Only about one fifth refused to conform at all.

Just to be certain that the result was due to the influence of the confederates responses and not to the difficulty of the task Ash used a control group. Each control subject was asked to make a judgement individually - there were no pressures at all. Over 90% gave correct responses.

Hollander and Willis give some criticisms of the early research into conformity. Firstly the studies do not identify the motive or type of conformity. Do the subjects conform in order to gain social approval? Are they simply complying? Do they really believe that their response is correct? Secondly Hollander and Willis claim that the experiments do not identify whether the subjects are complying because they judge that it"s not worth appearing to be different, or because the actually start to believe that the groups judgement is correct. Hollander and Willis also claim that the studies cannot show whether those who do not conform do so because they are independant thinkers or because they are anti-conformists. And Lastly, they claim that the studies seem to assume that independance has to be good and conformity has to be bad. However conformity is often benificial.

Sherif and Asch have each conducted fairly artificial laboritory experiments which showed that about 30% of responses can be explained by the need or desire of the subjects to conform. These experiments may not accurately reflect real life when conformity might be benificial and sometimes contribute to psychological well-being.