Final answer:
The Clever Hans study highlights the issue of experimenter bias, which can be controlled with a double blind procedure, where neither the participants nor the researchers know which group the participants are in.
Step-by-step explanation:
The study of Clever Hans is an example demonstrating how experimenter bias can influence the results of an experiment. One effective way to control for experimenter bias is through a double blind procedure. In this kind of study, both the participants and the researchers are blind to group assignments. This is critical for ensuring that both experimenter expectations and participant expectations do not affect the study's outcomes.
Double blind procedures are especially useful in clinical trials or any setting where the psychological effect of being in a study could influence the results. For instance, in a medical study, neither patients nor doctors know who receives the actual treatment and who receives a placebo. As a result, the outcomes can more reliably be attributed to the treatment itself rather than expectations about the treatment.