Final answer:
The correctly defined variable from the student's options is the confounding variable, which is a variable that affects the results of an experiment, but is not the main independent variable under study.
Step-by-step explanation:
In experimental studies, variables play a crucial role in determining the structure and outcomes of the experimentation. The statement "The confounding variable is a variable other than the independent variable that affects the results" is correct. A confounding variable is an external variable that can affect the results of an experiment, but it is not the variable that is being intentionally studied or manipulated. The independent variable is the one that is intentionally changed or manipulated by the experimenter to observe its effect on the dependent variable, but it is not the variable 'being observed by the experimenter' as incorrectly stated. The dependent variable, on the other hand, is the variable that is observed and measured to assess the effect of the independent variable; it is not the one that is manipulated, contrary to the erroneous statement. Control variables are factors that are kept constant and unchanging throughout the experiment in all conditions, not variables that must differ, as mentioned improperly in the prompt. They are essential to ensure that the results of the experiment are due to the manipulation of the independent variable alone.