Rotary oil rigs. An economist wants to compare the average monthly number of rotary oil rigs running in three states: California, Utah, and Alaska. In order to account for month-to-month variation, three months were randomly selected over a two-year period and the number of oil rigs running in each state in each month was obtained from data provided from World Oil

(Jan. 2002) magazine. The data, shown in the accompanying table, were analyzed by means of a randomized block design. The MINITAB printout is provided on the next page.

a. Why is a randomized block design preferred over a completely randomized design for comparing the mean number of oil rigs running monthly in California, Utah, and Alaska?

b. Identify the treatments for the experiment.
Supplementary Exercises 10.110–10.141 603 MINITAB Output for Exercise 10.120

c. Identify the blocks for the experiment.

d. State the null hypothesis for the ANOVA F-test.

e. Locate the test statistic and p-value on the MINITAB printout above. Interpret the results.

f. A Tukey multiple comparison of means (at a = .05)
is summarized in the SPSS printout below. Which state(s) have the significantly largest mean number of oil rigs running monthly?

Transcribed Image Text:

Month California Utah Alaska 3 228 123 27 17 34 36 1555 11 20 14 14