A researcher is interested in the effects of teaching styles on learning. She randomly assigns students to either a lecture-based class taught at 8:00 a.m. or a discussion-based class taught at 2:00 p.m. Her results reveal that students in the discussion-based class performed better than those in the lecture-based class. In this example, the time that the class is taught could make it impossible to establish a causal connection between teaching method and classroom performance. Time that the class is taught is which type of variable and why ?Explain