A personnel committee is evaluating professors. Professor X has the highest student ratings in the department. One of the committee members suggests that Professor X should receive the highest merit raise in the department. Another committee member raises an objection. She states, "Professor X scores are high, compared to other professors, because over half of the students drop out of Professor X's courses, not because Professor X is an excellent professor." What threat to the validity of the conclusion that Professor X is an excellent professor is the committee member describing? Group of answer choices maturation effect history effect testing effect differential attrition effect