Asch Conformity Line Experiment

Solomon Asch experimented with investigating the extent to which social pressure from a majority group could affect a person to conform.

He believed the main problem with Sherif’s (1935) conformity experiment was that there was no correct answer to the ambiguous autokinetic experiment.  How could we be sure that a person conformed when there was no correct answer?

Asch (1951) devised what is now regarded as a classic experiment in social psychology, whereby there was an obvious answer to a line judgment task.

If the participant gave an incorrect answer, it would be clear that this was due to group pressure.

Asch (1951) line study of conformity cartoon

Experimental Procedure

Asch used a lab experiment to study conformity, whereby 50 male students from Swarthmore College in the USA participated in a ‘vision test.’

Using a line judgment task, Asch put a naive participant in a room with seven confederates/stooges. The confederates had agreed in advance what their responses would be when presented with the line task.

The real participant did not know this and was led to believe that the other seven confederates/stooges were also real participants like themselves.

Asch experiment target line and three comparison lines

Each person in the room had to state aloud which comparison line (A, B or C) was most like the target line. The answer was always obvious.  The real participant sat at the end of the row and gave his or her answer last.

There were 18 trials in total, and the confederates gave the wrong answer on 12 trials (called the critical trials).  Asch was interested to see if the real participant would conform to the majority view.

Asch’s experiment also had a control condition where there were no confederates, only a “real participant.”


Asch measured the number of times each participant conformed to the majority view. On average, about one third (32%) of the participants who were placed in this situation went along and conformed with the clearly incorrect majority on the critical trials.

Over the 12 critical trials, about 75% of participants conformed at least once, and 25% of participants never conformed.

In the control group, with no pressure to conform to confederates, less than 1% of participants gave the wrong answer.


Why did the participants conform so readily?  When they were interviewed after the experiment, most of them said that they did not really believe their conforming answers, but had gone along with the group for fear of being ridiculed or thought “peculiar.

A few of them said that they really did believe the group’s answers were correct.

Apparently, people conform for two main reasons: because they want to fit in with the group (normative influence) and because they believe the group is better informed than they are (informational influence).

Critical Evaluation

One limitation of the study is that is used a biased sample. All the participants were male students who all belonged to the same age group. This means that the study lacks population validity and that the results cannot be generalized to females or older groups of people.

Another problem is that the experiment used an artificial task to measure conformity – judging line lengths. How often are we faced with making a judgment like the one Asch used, where the answer is plain to see?

This means that the study has low ecological validity and the results cannot be generalized to other real-life situations of conformity. Asch replied that he wanted to investigate a situation where the participants could be in no doubt what the correct answer was. In so doing he could explore the true limits of social influence.

Some critics thought the high levels of conformity found by Asch were a reflection of American, 1950’s culture and told us more about the historical and cultural climate of the USA in the 1950s than then they do about the phenomena of conformity.

In the 1950s America was very conservative, involved in an anti-communist witch-hunt (which became known as McCarthyism) against anyone who was thought to hold sympathetic left-wing views.

Conformity to American values was expected. Support for this comes from studies in the 1970s and 1980s that show lower conformity rates (e.g., Perrin & Spencer, 1980).

Perrin and Spencer (1980) suggested that the Asch effect was a “child of its time.” They carried out an exact replication of the original Asch experiment using engineering, mathematics and chemistry students as subjects. They found that in only one out of 396 trials did an observer join the erroneous majority.

Perrin and Spencer argue that a cultural change has taken place in the value placed on conformity and obedience and in the position of students. In America in the 1950s, students were unobtrusive members of society, whereas now they occupy a free questioning role.

However, one problem in comparing this study with Asch is that very different types of participants are used. Perrin and Spencer used science and engineering students who might be expected to be more independent by training when it came to making perceptual judgments.

Finally, there are ethical issues: participants were not protected from psychological stress which may occur if they disagreed with the majority.

Evidence that participants in Asch-type situations are highly emotional was obtained by Back et al. (1963) who found that participants in the Asch situation had greatly increased levels of autonomic arousal.

This finding also suggests that they were in a conflict situation, finding it hard to decide whether to report what they saw or to conform to the opinion of others.

Asch also deceived the student volunteers claiming they were taking part in a “vision” test; the real purpose was to see how the “naive” participant would react to the behavior of the confederates. However, deception was necessary to produce valid results.

The clip below is not from the original experiment in 1951, but an acted version for television from the 1970s.

Factors Affecting Conformity

In further trials, Asch (1952, 1956) changed the procedure (i.e., independent variables) to investigate which situational factors influenced the level of conformity (dependent variable).

His results and conclusions are given below:

Group Size

Asch (1956) found that group size influenced whether subjects conformed. The bigger the majority group (no of confederates), the more people conformed, but only up to a certain point.

With one other person (i.e., confederate) in the group conformity was 3%, with two others it increased to 13%, and with three or more it was 32% (or 1/3).

Optimum conformity effects (32%) were found with a majority of 3. Increasing the size of the majority beyond three did not increase the levels of conformity found. Brown and Byrne (1997) suggest that people might suspect collusion if the majority rises beyond three or four.

According to Hogg & Vaughan (1995), the most robust finding is that conformity reaches its full extent with 3-5 person majority, with additional members having little effect.

Lack of Group Unanimity / Presence of an Ally

As conformity drops off with five members or more, it may be that it’s the unanimity of the group (the confederates all agree with each other) which is more important than the size of the group.

In another variation of the original experiment, Asch broke up the unanimity (total agreement) of the group by introducing a dissenting confederate.

Asch (1956) found that even the presence of just one confederate that goes against the majority choice can reduce conformity as much as 80%.

For example, in the original experiment, 32% of participants conformed on the critical trials, whereas when one confederate gave the correct answer on all the critical trials conformity dropped to 5%.

This was supported in a study by Allen and Levine (1968). In their version of the experiment, they introduced a dissenting (disagreeing) confederate wearing thick-rimmed glasses – thus suggesting he was slightly visually impaired.

Even with this seemingly incompetent dissenter, conformity dropped from 97% to 64%. Clearly, the presence of an ally decreases conformity.

The absence of group unanimity lowers overall conformity as participants feel less need for social approval of the group (re: normative conformity).

Difficulty of Task

When the (comparison) lines (e.g., A, B, C) were made more similar in length it was harder to judge the correct answer and conformity increased.

When we are uncertain, it seems we look to others for confirmation. The more difficult the task, the greater the conformity.

Answer in Private

When participants were allowed to answer in private (so the rest of the group does not know their response), conformity decreased.

This is because there are fewer group pressures and normative influence is not as powerful, as there is no fear of rejection from the group.


Allen, V. L., & Levine, J. M. (1968). Social support, dissent and conformity. Sociometry, 138-149.

Asch, S. E. (1951). Effects of group pressure upon the modification and distortion of judgment. In H. Guetzkow (ed.) Groups, leadership and men. Pittsburgh, PA: Carnegie Press.

Asch, S. E. (1952). Group forces in the modification and distortion of judgments.

Asch, S. E. (1956). Studies of independence and conformity: I. A minority of one against a unanimous majority. Psychological monographs: General and applied, 70(9), 1-70.

Back, K. W., Bogdonoff, M. D., Shaw, D. M., & Klein, R. F. (1963). An interpretation of experimental conformity through physiological measures. Behavioral Science, 8(1), 34.

Bond, R., & Smith, P. B. (1996). Culture and conformity: A meta-analysis of studies using Asch’s (1952b, 1956) line judgment task. Psychological bulletin119(1), 111.

Longman, W., Vaughan, G., & Hogg, M. (1995). Introduction to social psychology.

Perrin, S., & Spencer, C. (1980). The Asch effect: a child of its time? Bulletin of the British Psychological Society, 32, 405-406.

Sherif, M., & Sherif, C. W. (1953). Groups in harmony and tension. New York: Harper & Row.

Olivia Guy-Evans

BSc (Hons), Psychology, MSc, Psychology of Education

Associate Editor for Simply Psychology

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

Saul Mcleod, PhD

Educator, Researcher

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul Mcleod, Ph.D., is a qualified psychology teacher with over 18 years experience of working in further and higher education.