Asch Line Experiment

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Imagine yourself in the following situation: You sign up for a psychology experiment, and on a specified date you and seven others whom you think are also participants arrive and are seated at a table in a small room.

You don't know it at the time, but the others are actually associates of the experimenter, and their behavior has been carefully scripted. You're the only real participant.

The experimenter arrives and tells you that the study in which you are about to participate concerns people's visual judgments. She places two cards before you.

asch (1951) line study of conformity

The card on the left contains one vertical line. The card on the right displays three lines of varying length.

The experimenter asks all of you, one at a time, to choose which of the three lines on the right card matches the length of the line on the left card. The task is repeated several times with different cards.

On some occasions the other "participants" unanimously choose the wrong line. It is clear to you that they are wrong, but they have all given the same answer.

What would you do? Would you go along with the majority opinion, or would you "stick to your guns" and trust your own eyes?

If you were involved in this experiment how do you think you would behave? Would you conform to the majority’s viewpoint?

Asch believed that 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.

Study Description


Solomon Asch (1951) conducted an experiment to investigate the extent to which social pressure from a majority group could affect a person to conform.


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.

asch (1951) line study of conformity

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 participants were also real participants like themselves.

asch (1951) line study of conformity

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 trails (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 participant 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 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.

This means that study has low ecological validity and the results cannot be generalized to other real life situations of conformity.

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

Asch 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 Asch (1951) study has also been called a child of its time (as conformity was the social norm in 1950’s America). The era of individualism, ‘doing your own thing’, did not take hold until the 1960s.

Perrin and Spencer (1980) carried out an exact replication of the original Asch experiment using British engineering, mathematics and chemistry students as participants.

The results were clear cut: on only one out of 396 trials did a participant conform with the incorrect majority. This shows the Asch experiment has poor reliability.

Video Clip

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) in order to investigate which 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 3 did not increase the levels of conformity found. Brown and Byrne (1997) suggest that people might suspect collusion if the majority rises beyond 3 or 4.

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 5 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 introduced 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 this conformity dropped to 5%.

This was supported in a study by Allen & 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 participant 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 decreases.

This is because there is less groups pressure 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.

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.

How to cite this article:

McLeod, S. A. (2008). Asch Experiment. Retrieved from

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