Which of the following threat to internal validity was identified by Ronsenthal in 1966?

Correct option is C

The correct answer is Expectancy. In 1966, Robert Rosenthal identified the Expectancy Effect, also known as the Rosenthal Effect or Pygmalion Effect, as a threat to internal validity in experimental research. This effect refers to the phenomenon where the experimenter's expectations about the outcome of an experiment can influence the behavior of the participants, potentially biasing the results. Rosenthal's work showed that researchers' preconceived notions or expectations could subtly influence how they interact with participants or how they interpret their responses, ultimately affecting the study's outcomes. This psychological phenomenon occurs when researchers unknowingly give cues or signals to participants about how they should behave, which then leads to participants fulfilling these expectations.
Information Booster:
Expectancy Effect (Rosenthal Effect) The expectancy effect, as identified by Rosenthal, occurs when researchers unintentionally influence the results of an experiment based on their expectations of the outcome. For instance, if an experimenter believes a certain treatment or intervention will yield positive results, they may behave in a way that encourages or rewards behaviors consistent with that expectation, leading to biased results. This phenomenon is especially pronounced when the researcher is unaware of how their beliefs are influencing the experiment.
Sources:
Rosenthal, R. (1966). Experimenter Effects in Behavioral Research. Psychological Bulletin, 66(6), 37–46.
Rosenthal, R. (1994). Influence: Science and Practice. Allyn & Bacon.
Additional Information (Incorrect Options):
(a) Maturation Maturation refers to the natural changes that occur in participants over time during an experiment. These changes could be biological, psychological, or developmental, and they might affect how participants respond to the treatment or conditions of the experiment. While maturation can threaten internal validity, it was not the threat identified by Rosenthal in 1966.
(b) Instrumentation Instrumentation refers to changes in the measurement instruments or tools used during an experiment that might influence the outcome. If the instrument or method of measurement is not consistent throughout the experiment, it can affect the results. However, this is a different kind of threat to internal validity than expectancy effects, as it concerns the tools used rather than the experimenter's expectations.
(d) Experimental Mortality Experimental mortality, also known as attrition, refers to the loss of participants during the course of an experiment, which can affect the generalizability and validity of the results. While this is a valid threat to internal validity, it was not the focus of Rosenthal's 1966 research on expectancy effects.