Conjunction Fallacy (Conjunction Error)

A conjunction fallacy occurs when two events that can occur together or separately are seen as more likely to occur together than separately. This usually happens when it is easier to imagine two events occurring in a combination than occurring alone. Consider the following statements and decide which is more likely: 1) Carol has several students that practice the piano everyday; or 2) Her students that practice the piano everyday are proficient. Of these two statements, the first statement is more likely. The amount of students that are proficient and practice the piano is not the same as the probability that her students are either proficient or practice the piano.