What cognitive bias involves the overestimation of the number of people who share our beliefs?

The cognitive bias that involves the overestimation of the number of people who share our beliefs is known as the False Consensus Effect. This phenomenon occurs because individuals often project their own opinions, values, and behaviors onto others, leading to the assumption that these are more widely held than they actually are.

For instance, if someone strongly believes in a particular political stance, they might assume that most other people also hold that same belief, which can reinforce their confidence in their views and reduce exposure to opposing perspectives. This effect can have significant implications in social interactions and discussions, as it may create echo chambers where only similar viewpoints are acknowledged and discussed, thereby inhibiting open dialogue and critical thinking about contrasting ideas.

In contrast, Confirmation Bias refers to the tendency to search for or interpret information in a way that confirms one’s preexisting beliefs, rather than overestimating the consensus around them. Groupthink involves a group’s tendency to strive for consensus at the expense of critical thinking and individual opinions, leading to flawed decision-making. Self-Serving Bias is the habit of attributing positive outcomes to oneself while blaming negative outcomes on external factors, which does not directly relate to the perception of others' beliefs.