When a researcher's expectations affect the outcome of a study, what is this phenomenon called?

The phenomenon where a researcher's expectations influence the outcome of a study is known as experimenter bias. This type of bias occurs when a researcher inadvertently affects participants' behavior or the data collection process due to their preconceived notions or hypotheses about the study's outcome. For example, if a researcher expects a particular treatment to be effective, they may unconsciously interact with the participants in a way that encourages those expected outcomes, or they might interpret ambiguous data in line with their expectations.

Experimenter bias can be particularly problematic as it may lead to results that are not a true reflection of reality but rather a reflection of the researcher's beliefs or desires. To minimize this bias, researchers often employ double-blind study designs, where neither the participants nor the experimenters know which group receives the treatment and which receives a placebo until after the data is collected. This helps ensure that the outcome of the study is driven by the variable being tested rather than the researcher’s influence.

The other options refer to different types of bias: selection bias relates to how participants are chosen for a study, confirmation bias involves focusing on evidence that confirms existing beliefs, and response bias pertains to the way respondents may provide inaccurate or misleading answers on surveys or assessments. Each of these biases impacts research but