Question

A scientist told his student assistants that he had sorted groups of mice by their intelligence and asked the assistants to assess the groups’ maze-solving abilities. The scientist had not actually sorted the mice by intelligence. The students rated the “highest intelligence” group of mice as the best maze solvers and the “lowest intelligence” group as the worst maze solvers. What was the scientist trying to demonstrate by doing this experiment?
Experimental subjects should never be put into groups.
Mice should not be judged by their intelligence.
Higher intelligence mice are better maze solvers.
People can introduce their own biases into an experiment.

Answer 1

People can introduce their own biases into an experiment.

This demonstrates the observer-expectancy (Rosenthal) effect: the students' expectations influenced their assessments, so blind or double-blind procedures are needed to prevent such bias.