Final answer:
The most appropriate operational definition of the independent variable in Timothy's study on stress and test performance is a. whether the participant is told that the test score counts for a large or small percentage of the grade. This manipulation directly impacts perceived stress, unlike outcomes or observations, which are dependent variables.
Step-by-step explanation:
In the context of Timothy's research question, the most appropriate operational definition of the independent variable, which is the factor being manipulated to test its effect on stress levels on test performance, is: whether the participant is told that the test score counts for a large or small percentage of course grade. This operational definition directly manipulates the perceived stress level by altering the stakes of the test, which can be controlled and measured by the researcher. This variable is independent because it is not affected by the participant's behavior but rather influences it.
Options b, c, and d are not suitable as they relate to the outcomes of the test (which are dependent variables) or subjective observations, rather than factors that the researcher can actively control.
Other parts of multiple-choice questions provided in the student's question refer to different statistical concepts. The term 'dependent means' (C.) from choice 121 relates to paired data where two sets of scores come from the same group of participants, thereby implying a dependency between the measures. It is essential for the researcher to have clear and rigorous operational definitions for all variables to ensure the reliability and validity of the study.