Final answer:
The independent variable in Mary's experiment is the type of learning strategy employed, which is either active or passive. This variable is what is being manipulated to observe its effect on the test scores of the students, which serve as the dependent variable.
Step-by-step explanation:
The independent variable in Mary's study to determine if active learning strategies promote better student learning than passive learning strategies is the type of learning strategy used (active vs. passive). In experimental studies, the independent variable is the factor that is manipulated or controlled by the experimenter to observe its effects on the dependent variable, which in this case would be the number of items each student answers correctly on the test.
An independent variable is a crucial component of a research design because it represents the factor that is hypothesized to cause a change in the dependent variable. In Mary's experiment, she is testing the hypothesis that active learning strategies will lead to better student learning outcomes as measured by the students' test scores. Examples of active learning include student discussions, problem-based learning, and other interactive techniques, whereas examples of passive learning might include listening to lectures or reading textbooks without engagement.