Participation in a company’s walking program. A study was conducted to investigate the effect of prompting in a walking program instituted at a large corporation (Health Psychology, March 1995). Five groups of walkers—27 in each group—agreed to participate by walking for 20 minutes at least one day per week over a 24-week period. The participants were prompted to walk each week via telephone calls, but different prompting schemes were used for each group. Walkers in the control group received no prompting phone calls; walkers in the “frequent/low” group received a call once a week with low structure (i.e., “just touching base”); walkers in the “frequent/high” group received a call once a week with high structure (i.e., goals are set); walkers in the “infrequent/ low” group received a call once every 3 weeks with low structure; and walkers in the “infrequent/high” group received a call once every 3 weeks with high structure. The table at the bottom of the page lists the number of participants in each group who actually walked the minimum requirement each week for weeks 1, 4, 8, 12, 16, and 24. The data were subjected to an analysis of variance for a randomized block design, with the five walker groups representing the treatments and the six time periods (weeks) representing the blocks.

a. What is the purpose of blocking on weeks in this study?

b. Fill in the missing entries on the ANOVA summary table shown.

c. Is there sufficient evidence of a difference in the mean number of walkers per week among the five walker groups? Use  = .05.

d. Tukey’s technique was used to compare all pairs of treatment means with an experimentwise error rate of  = .05. The rankings are shown at the bottom of the page. Interpret these results.

e. What assumptions must hold to ensure the validity of the inferences in parts c and d?

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