Kruskal-Wallis Tests in SPSS STAT 314
Three teaching methods were tested on a group of 19 students with homogeneous backgrounds in
statistics and comparable aptitudes. Each student was randomly assigned to a method and at the end of a
6-week program was given a standardized exam. Because of classroom space and group size, the
students were not equally allocated to each method. The results are shown in the table below. Test for a
difference in distributions (medians) of the test scores for the different teaching methods using the
Kruskal-Wallis test.
Method 1
94
87
90
74
86
97
Method 2
82
85
79
84
61
72
80
Method 3
89
68
72
76
69
65
1. Enter the time values into one variable and the corresponding teaching method number (1 for
Method 1, 2 for Method 2, 3 for Method 3) into another variable (see figure, below). Be sure to
code your variables appropriately.
2. Now it is time to check the assumption of same shape for the treatment distributions. Select
Graphs Legacy Dialogs Boxplot… (be sure the type is “Simple” and the data in the chart
are “Summaries for groups of cases”) with “Test Score” as the variable measured and “Teaching
Method” as the category axis variable (see figures, below). Click “OK”. You may double-click
the resulting boxplot to access the chart editor and adjust any display settings as desired
(background color, bar width, bar color, etc.). As long as the boxes have approximately the same
shape, you may continue with the Kruskal-Wallis procedure.
