Suppose an instructor is also a researcher who wants to know if engaging students in a research project of their own can increase their overall critical thinking. She decides to test this using students in her own class. Specifically, the instructor allows students to choose either to conduct their own research or to simply take the final exam. At the end of the semester, she tests students' critical thinking by giving them a survey. She then, compares the scores of those who conducted their own research with the ones who simply opted in to take the final exam. In addition, the researcher included included the overall grade that each student received in the class to rule out the possibility that the overall performance the class was the cause of higher critical thinking scores. The overall performance in the class is potentially_______________________________
Group of answer choices
a confounding variable
an independent variable
an experimental condition
a dependent variable