Solomon Asch’s 1951 line-judgment experiment demonstrated conformity to group pressure.
Participants compared the length of a standard line with three comparison lines. The correct choice was usually obvious. However, several other people in the room were confederates who deliberately gave the same wrong answer on selected trials. Some participants then agreed with the group even when the group’s judgment visibly conflicted with the lines.
Asch’s original work found that participants conformed to the incorrect majority on about one-third of the critical trials, while 75 percent conformed at least once. In a control condition without group pressure, errors were rare.
The study measured public agreement, not permanent changes in private perception. Many participants later said they knew the group was wrong but did not want to appear different, while others doubted their own judgment. Group size, unanimity, and the presence of a dissenting ally influenced conformity.