Asch carried out several variations of his original study to investigate how group size, unanimity and task difficulty affect conformity.

One variable he investigated was group size. He used between 1 and 15 confederates and found that conformity increased as group size increased, but only up to a point. Conformity peaked at about 31.8% with three confederates and then remained fairly stable. This suggests that a majority of three is enough to create pressure to conform, most likely through normative social influence.

Asch also investigated unanimity. In one variation, one confederate gave the correct answer, which reduced conformity to 5%. In another, one confederate gave a different wrong answer, reducing conformity to 9%. These findings show that when the group is no longer unanimous, conformity drops sharply because the participant feels more able to resist the majority.

Finally, Asch investigated task difficulty by making the line lengths more similar, so the correct answer was less obvious. He found that conformity increased as the task became more difficult. This suggests that when people are unsure, they are more likely to look to others for guidance, showing the role of informational social influence.

One limitation of Asch's research is that it lacks ecological validity. The line judgement task was artificial and unlike the kinds of conformity people experience in everyday life. Real-life conformity often involves more meaningful situations, such as pressure from friends or wider social groups, where the consequences may feel much more important. This means participants may have behaved differently in Asch's study than they would in real social situations. Therefore, the findings may not accurately reflect conformity in everyday life.

Another limitation is that Asch's study lacks population validity. The sample consisted of 123 male American college students from Swarthmore College in the 1950s. This is a very narrow sample, so the findings cannot automatically be generalised to women or to people from different cultures and time periods. Later research has suggested that cultural background and gender can influence conformity levels. Therefore, Asch's findings may not be representative of conformity in the wider population.

However, one strength of Asch's research is that it was carried out in a highly controlled laboratory setting, which meant the study was also easy to replicate. Standardised procedures and identical materials were used, so all participants experienced the same conditions and extraneous variables were well controlled. This increases the internal validity of the study because changes in conformity are more likely to have been caused by social pressure rather than other factors. It also means that other researchers could repeat the procedure to check the consistency of the findings. For example, Perrin and Spencer were able to replicate Asch's study in a different context and compare the results. This suggests that Asch's research was scientifically rigorous and provided a strong foundation for later research into conformity.