Concept explainers
Treating alcoholics The nonparametric statistics textbook by Hollander and Wolfe (1999) discussed a study on a social skills training program for alcoholics. A sample of male alcoholics was randomly split into two groups. The control group received traditional treatment. The treatment group received the traditional treatment plus a class in social skills training. Every two weeks for a year after the treatment, subjects indicated the quantity of alcohol they consumed during that period. The summary response was the total alcohol intake for the year (in centiliters).
- a. Suppose the researchers planned to conduct a one-sided test and believed that the response variable could be highly skewed to the right. Why might they prefer to use the Wilcoxon test rather than a two-sample t test to compare the groups?
- b. The data were
Controls: 1042, 1617, 1180, 973, 1552, 1251, 1151, 1511, 728, 1079, 951, 1319
Treated: 874, 389, 612, 798, 1152, 893, 541, 741, 1064, 862, 213
Show how to find the ranks and the mean ranks for the two groups.
- c. MINITAB reports the results shown in the output below. Report and interpret the P-value.
- d. Report and interpret the confidence interval shown in the output.
MINITAB output
Point estimate for η1 − η2 is 435.5 95.5 Percent CI for η1 − η2 is (186.0, 713.0) Test of η1 = η2 vs η1 ≠ η2 is significant at 0.0009
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Chapter 15 Solutions
EP STATISTICS:ART+SCI...-MYLABSTATISTIC
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