How many feet do you have to stop away from rail road crossing

Dr. dow jones wants to know whether a problem-based approach to teaching economics will result in higher academic performance than his traditional method. of the six sections of economics 101 at his university, dr. jones randomly assigns three sections to the traditional method and three sections to the problem-based method for unit 1 of the course. then all sections switch the instructional method for unit 2. he plans to compare the performance of the two groups of sections on their unit 1 and unit 2 exams. this study employs a design.