Chapter 14

1. Why are within-subjects designs usually more powerful than between-subjects design?

2. What source of variation is found in an ANOVA summary table for a within-subjects design that is not in in an ANOVA summary table for a between-subjects design. What happens to this source of variation in a between-subjects design?

3. Compute an ANOVA for the following data. Test all differences between means using the Tukey test at the .01 level. The three scores per subject are their scores on three trials of a memory task.

4 6 7
3 7 7
2 8 5
1 4 7
4 6 9

4. Test the linear and quadratic components of trend for the data in problem 3.

5. Give the source and df columns of the ANOVA summary table for the following experiments:
a. Twenty subjects are each tested on a simple reaction time task and on a choice reaction time task.
b. Ten male and 10 female subjects are each tested under three levels
of drug dosage: 0 mg, 10 mg, and 20 mg.
c. Twelve subjects are tested on a motor learning task for three trials a day for two days.
d. An experiment is conducted in which depressed people are either assigned to a drug therapy group, a behavioral therapy group, or a control group. Ten subjects are assigned to each group. The level of measured once a month for four months.

6. The dataset "Stroop" has the scores (times) for males and females on each of three tasks:

  1. Subjects read the names of colors printed in black ink.
  2. Subjects name the colors of rectangles.
  3. Subjects are given the names of colors written in ink of different colors. For example, blue might be written in red ink.

a. Do an analysis of variance.
b. Test all pairwise comparisons among the three conditions using the Tukey test at the .01 level.

7. Subjects threw darts at a target. In one condition, they used their preferred hand; in the other condition they used their other hand. All subjects in performed in both conditions (the order of conditions was counterbalanced). Their scores are shown below. Test the difference between conditions once using a t-test and once using one-way analysis of variance. What is the relationship between the t and the F?

preferred hand Non-preferred hand
  12                  7
   7                  5
  12                  8
  13                 10

8. Assume the data in Problem 7 were collected using two different groups of subjects: One group used their preferred hand and the other group used their non-preferred hand. Analyze the data and compare the results to those for problem 7.

9. When should a within-subjects design be avoided?

Selected Answers