Pig bile study. Bear gallbladder is used in Chinese medicine to treat inflammation. A study in the Journal of Ethnopharmacology (June 1995) examined the easier-to-obtain pig gallbladder as an effective substitute for bear gallbladder. Twenty male mice were divided randomly into two groups: Ten were given a dosage of bear bile and 10 were given a dosage of pig bile. All the mice then received an injection of croton oil in the left earlobe to induce inflammation. Four hours later, both the left and right earlobes were weighed, with the difference (in milligrams) representing the degree of swelling. Summary statistics on the degree of swelling are provided in the following table:
Bear Bile ..... Pig Bile
n1 = 10 ...... n2 = 10
x̄1 = 9.19 ... x̄2 = 9.71
σ1 = 4.17 .... σ2 = 3.33
a. Use a hypothesis test (at α = .05) to compare the variation in degree of swelling for mice treated with bear bile and mice treated with pig bile.
b. What assumptions are necessary for the inference you made in part a to be valid?

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