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, 3 months were randomly selected over a 2-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, were analyzed using a randomized block design.

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. Locate the test statistic and /?-value on the XLSTAT printout shown below. Interpret the results.

f. A Tukey multiple comparisons of means (at α = .05) is summarized in the XLSTAT printout below. Which state(s) have the significantly largest mean number of oil rigs running monthly?
XLSTAT output for Exercise 9.58f
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Month California Utah Alaska 27 34 36 14 14 Analysis of variance Source DF Sum of squares Model Error Correctecd Computed against model Y Mean() Mean squares 648 4444 32 4444 Type li Sum of Squares analysis Source OF Sum of squares Mean squares F Pr F State Month 617 5556 30.8889 08 7778 38 085 0.002 15 4444 19041 02 State / Tukey (HSD) / Analysis of the differences between the categories with a confidence interval of 95% CAL VS AL 19.3333 CAL VS UT 15.0000 UT vs AL 4.3333 Tukey's d critical value Contrast Difference Standardized difference Critical value Pr Diff Significant 8.3140 6.4505 1.8635 Yes Yes No 3.5641 0.0025 3.56410.0066 5.0404 Category Mean CAL UT AL Groups 32.3333 17.3333 13,0000