What famous example illustrates experimenter bias?

Clever Hans serves as a well-known illustration of experimenter bias, which occurs when a researcher's expectations or beliefs unintentionally influence the outcomes of an experiment. In the case of Clever Hans, a horse was believed to be able to perform complex arithmetic and answer questions by tapping his hoof. The horse gained widespread attention and was thought to possess extraordinary abilities.

However, upon investigation, it became evident that Clever Hans was not actually performing calculations but rather responding to subtle cues given by his trainer or other observers. The trainer himself was unaware of his influence on the horse's behavior, which highlights how expectations can inadvertently alter the results of an experiment. This example demonstrates the importance of controlling for biases in research to ensure that findings accurately reflect reality rather than the unintentional effects of the observer or experimenter.

Other options, while notable in their own right, do not specifically exemplify the concept of experimenter bias in the same manner. Cold fusion refers to a controversial claim about nuclear reactions at room temperature, spontaneous generation is the disproven idea that life arises from non-living matter, and the static universe theory relates to cosmological views before the acceptance of the expanding universe model. None of these directly showcase the influence of an experimenter's expectations on experimental