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An instructor at a community college is interested in examining a set of score changes between a pair of tests given in one of his college courses. He issued a pretest on the first day of class, and after a few weeks of lecture he issued a posttest on the same material. The instructor recorded the scores on both tests, as well as the difference in scores (posttest-pretest) for each student.

Perform the Wilcoxon signed rank test to determine whether there is evidence that the scores on the posttest were different than those on the pretest for the students.

SAS Institute Inc.

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The Score data set contains data about pretest and postest scores for students in a college course.

These are the variables in the data set:

This data is sample data from SAS Institute Inc.

The value of the sign test statistic is M = -1, with a p-value of 0.7744. This gives insufficient evidence of a significant difference between pretest and posttest scores for the students.

An experiment was conducted in which electrical measurements were taken on 24 wiring boards. Each board was measured first when soldering was completed, and again after three weeks in a chamber with a controlled environment of high temperature and humidity.

The Shapiro-Wilk W test for Normality for the data yielded a p-value of 0.0076, indicating that the data are significantly non-Normal. Use the Wilcoxon signed-rank test to determine if there is a significant difference (at level α = 0.05) between the outside and inside chamber measurements.

Lee Creighton (modified by Paris Faison)
SAS Institute Inc.

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The Chamber data set represents electrical measurements on 24 wiring boards. Measurements were taken both outside and inside a chamber, and the difference between these measurements (outside – inside) was also recorded.

These are the variables in the data set:

Sall, J., Creighton, L., & Lehman, A. (2006). JMP Start Statistics, Third Edition. Cary, NC: SAS Institute Inc.

Using the UNIVARIATE procedure in SAS, the analysis variable for this procedure is the variable diff, which is calculated as outside – inside. The Wilcoxon signed-rank test gives a p-value of 0.0106, which gives evidence of a significant difference between the outside and inside chamber measurements (at the α = 0.05 level).