In the 1950's, a man by the name of Solomon Asch tried to understand and evaluate group think. He performed a series of studies which would come to be known as the Asch Conformity Experiments.
What Solomon did was have a group of students come together for a vision test. In actuality, all but one of the volunteers were in on the study, and there was only one person who was the focal point of the study. How will the views of the group affect the individual?

The way the experiment was set up. All of the students were in a classroom. They were asked a variety of questions about a group of lines (e.g. "which is the longest?", "which lines are equal in length?" etc) and the group had to give their answers aloud. The only person who was actually the focus of the study always had to go last. The group participants always gave the same answer. Sometimes correct, sometimes incorrect, but always the same answer... and slowly they started giving more and more wrong answers. When there was no pressure to conform, only 1 out of 35 participants ever gave a wrong answer. When, the study's focus was surrounded by fellow students all giving the wrong answer, that student gave the same incorrect answer 36.8% of the time... and 75% of the students being studied gave an incorrect answer (going along with the group) at least once.
There were later variations of the experiment seeing just how many "confederates" were needed to coerce conformity, examing the influence of one... to as many as 15 people in on the study. When one or two people gave the wrong answer, their influence on the focal point of the study was almost none.
When the people who are in on the study are not unanimous, even when it was only 1 dissenting voice, the study focus was much more likely to give the obvious correct answer. Even if the 1 dissenter gave another incorrect answer, it still made the study focus more likely to give the correct answer, which was at odds with the rest of the students, showing how much influence a dissenting minority can have.
Interesting...