1. Several years ago some colleagues and I did an experiment to see if Avon's Skin-so-Soft was as good as OFF in repelling mosquitoes. We recruited 10 students and randomly assigned one arm to Skin-so-Soft and one to OFF. They wandered the campus for four hours, and we counted the number of new mosquito bites on each arm.
The value of the Wilcoxon signed rank statistic is
A. W+ = 13.
B. W+ = 28.
C. W+ = 32.
2. An experiment is set up to compare the effects of two different treatments on the age at which a child first walks. Eleven children were randomly divided into two groups, five in group 1 and six in group 2. Children in the first group were given special walking exercises for 12 minutes per day beginning at 1 week and lasting 7 weeks. The second group of children received daily exercises but not the walking exercises administered to the first group. Progress was checked weekly and the ages in months when the children first walked are given below.
The Wilcoxon rank sum of the ranks for group 1 is
A. 18.5.
B. 15.5.
C. 15.0.
3. Some researchers have conjectured that stem-pitting disease in peach tree seedlings might be controlled with weed and soil treatment. An experiment was conducted to compare peach tree seedling growth with soil and weeds treated with one of two herbicides.
In a field containing 10 seedlings, six were randomly selected throughout the field and assigned to receive Herbicide A. The remaining seedlings were to receive Herbicide B. Soil and weeds for each seedling were treated with the appropriate herbicide, and at the end of the study period the height (in cm) was recorded for each seedling. The following results were obtained:
When ranking all the observations together, the observations at a height of 81 cm should each be assigned the rank
A. 7.5.
B. 8.0.
C. 8.5.