False Consensus Bias is the tendency of people to overestimate the level to which other people agree or share their beliefs, attitudes, and behaviours which leads to people thinking that others agree with them.
People also tend to overvalue their own opinions due to this bias. Since, people live or grow up in family or society where the thinking of the people are mostly similar, this bias starts developing. Further, if we are too much confident on an idea or viewpoint we fall prey into False Consensus Bias.
Researcher Lee Ross and his colleagues studied and came up with the term “False Consensus Effect or Bias”.
They asked students at Stanford University to walk around the campus for half an hour wearing a large sandwich board that read “Repent,” counting the number of people who spoke with them while they walked around wearing the sign. They wanted to compare the students who said yes and who said no. they found that students who agreed to do this unusual request believed that a clear majority of other students would also agree to do so. But the students who to do so believed that a clear majority of other students would also refuse. This tendency is known as the false consensus effect.
It was concluded that people often believe that there is more consensus—that is, more agreement—for what we say, think, and do than is really the case.
Ross, L., Greene, D., & House, P. (1977). The false consensus effect: An egocentric bias in social perception and attribution processes. Journal of Experimental Social Psychology, 13, 279–301.