Final answer:
Participant expectancy can be affected by demand characteristics and the Rosenthal effect, both of which involve participants altering their behavior based on their perceptions of the experiment's purpose. Use of placebos is one strategy to mitigate these effects.
Step-by-step explanation:
Participant expectancy can be caused by demand characteristics. This term refers to any potential cues or features in an experiment that suggest to participants what the purpose is and what responses are expected or desired by the researchers. When participants form an understanding of the experiment's hypothesis, they may alter their behavior in ways that confirm the hypothesis, thus influencing the outcome of the research. The Rosenthal effect, also known as experimenter expectancy, is another concept related to participant expectancy where the researcher's expectation can affect the outcome of the experiment due to subtle, possibly subconscious cues given to participants. Utilizing a placebo in experiments is a common method to counteract participant expectancy effects.
The observer expectancy effect refers to a similar concept where the researcher's expectations may influence the results; however, observer expectancy primarily influences how researchers perceive and interpret outcomes, rather than the participants' behavior. Multiple dependent variables, multiple control groups, and the use of statistical analysis are not directly responsible for creating participant expectancy, although they are important elements in research design for addressing other types of variables and biases.