Answer to Question 1
B
Answer to Question 2
D
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Researchers seek to control confounding (or extraneous) variablesvariables that are extraneous to the purpose of a specific study but that might contaminate the results because they may be the actual cause or influence on the dependent variable. In this case, length of stay in the hospital may be the actual cause or at least one cause of the level of stress, instead of the cardiac surgery. The dependent variable is the behavior, characteristic, or outcome the researcher is interested in explaining, predicting, or affecting, which in this case is level of stress. The independent variable is the presumed cause of or influence on the dependent variable, which is cardiac surgery, in this case. The independent variable corresponds to the I and the C components in the PICO scheme. A mediating variable is a factor through which another factor has an effect on a dependent variable. In this case, for example, the effect of cardiac surgery on stress is mediated by length of stay, making length of stay the mediating factor.