Chapter 18, Problem 20P

In Problem 14 in Chapter 11, we described a study Showing that students are likely to improve their test

Scores if they go back and change answers after reconsidering some of the questions on the exam (Johnston, 1975). In the study, one group of students was encouraged to reconsider each question and

to change answer whenever they felt it was appropriate ate. The students were asked to record their original answers as well as the changes. For each student, the exam was graded based on the original answers and on the changed answers. For a group of n = 40 students

oppose that 26 had higher scores for the changed­ answer version and only 14 had higher scores for

the original-answer version. Is this result significantly

different from chance? Use a two-tailed test with a = .01.

There is some evidence suggesting that you are likely to improve your test score if you rethink and change answers on a multiple-choice ex am, (Johnston, 1975). To determine this phenomenon a teacher gave the same final exam to two section of a psychology course. The students in one section were told to tum in their exams immediately after finishing, without changing any of their answer. In the other section, students were encouraged to reconsider each question and to change answers whenever they felt it was appropriate. Before the final exam, the teacher had matched 9 students in the first section with 9 students in the second section based on their midterm grades. For example, a student in the no-change section with an 89 on the midterm exam was matched with student in the change section who also had an 89 on the midterm. The difference between the two final exam grades for each matched pair was computed and the data showed that the students who were allowed to change answers scoring higher by an average of MD = 7 point With SS = 288.

1. Do the data indicate a significant difference between the two conditions? Use a two-tailed test with a = .05.
2. Construct a 95% confidence interval to estimate the size of the population mean difference.

Write a sentence demonstrating how the result of the hypothesis test and the confidence interval would appear in a research report.