Researchers at the University of California Earthquake Center want to compare intensities of earthquakes at San Francisco Bay and at the Los Angeles Basin. The data, assumed to be independent random samples from the two areas, represent intensity on the Richter scale of tremors felt during several months in 1994.

(a) If researchers want to test if mean intensities differ between the two regions, state the appropriate null and alternative hypotheses.

(b) Use the two-sample t statistic in the output to characterize the p-value:

(i) extremely small

(ii) somewhat small

(iii) borderline

(iv) not small at all

(c) Is there statistically significant evidence of a difference?

(d) Would you expect a confidence interval for difference in population means to contain zero? (e) Are your conclusions still valid if one of the data sets is very skewed?

(f) Circle the part of the output that would help you decide if the Rule of Thumb for use of a pooled procedure is satisfied.

Output:

Two-sample T for SF vs LA N Mean StDev SE Mean SF 14 2.59 1.02 0.27 LA 16 2.13 1.09 0.27 Difference = mu SF - mu LA Estimate for difference: 0.454 %95% CI for difference: (-0.339, 1.248) T-Test of difference = 0 (vs not =): T-Value = 1.18