There is some evidence suggesting that you are likely to improve your test score if you rethink and change answers on a multiple-choice exam (Johnston, 1975). To examine this phenomenon, a teacher gave the same final exam to two sections of a psychology course. The students in one section were told to turn in their exams immediately after finishing, without changing any of their answers. In the other section, students were encouraged to reconsider each question and to change answers whenever they felt it was appropriate. The average score for the n = 20 students in the no-change section was M = 74.2 with SS = 460.6. The average for the n = 20 students in the change section was M = 78.6 with SS = 512.2.
Make a point estimate of the population mean difference between the two test conditions.