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, reproduced in the accompanying table and saved in the OILRIGS file, were analyzed by means of a randomized block design. The MINITAB printout is shown below (following the data).

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.

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 at the bottom of the previous column. Interpret the results.
f. A Tukey multiple comparison of means (at α = .05) is summarized in the SPSS printout at the bottom of the left column. Which state(s) have the significantly largest mean number of oil rigs running monthly?

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Month California Utah Alaska 27 34 36 17 20 15 Two-way ANOVA: NumRigs versus State, Month/Year Source State Month/ Year Error Total DF 2 617.556 308.778 38.07 0.002 30.889 5.444 1.90 0.2 62 4 32.444 8 680.889 S 2.848 R-Sq 95.23% R-Sq (adj) -90.47 # - Individual 95% C1 For Nean Based n Pooled StDev State AL 13.0000 CAL UT lean 32.3333 17.3333 16.0 24.0 32.0 40.0 NUMRIGS Tukey HSD Subset STATE 3 13,00 3 17.33 1 32.33 202 1.000 1,000 800 700 5 600 E 500 400 200 100 A B Box type