Conceptual Exercise 3.19 from the Sleuth page 79 (76 2nd edition), pdf copy. For each scenario, explain the source of dependence and whether the dependence is between or within groups. I expect to see a more thorough explanation than the answers at the end of the chapter.
These questions ask you to discuss the validity of the two sample t-test. You should comment on any evidence that the assumptions of Normality or equal standard deviations have been violated, and whether any robustness against the violations might be expected. Independence is also a crucial assumption but in these examples there isn’t quite enough information to evaluate it. You do not need to conduct the t-test
a) Using the data and from last homework
Examine the data and discuss the validity of the using a two sample t-test to compare the mean desired weight loss between those who exercised in the last month and those who didn’t. (I.e. was the t-test you conducted in the last homework valid?)
b) Exercise 1.25 in Sleuth contains data on Zinc concentrations in the blood of rats that received a dietary supplement and rats that did not receive the supplement.
Examine the data and discuss the validity of the using a two sample t-test to compare the mean zinc concentration between the two groups of rats.
c) Exercise 3.18 (pg 78) in the Sleuth gives metabolic expenditures for seven patients admitted to a hospital for multiple fractures (trauma) and eight patients admitted for other reasons (non-trauma).
Examine the data and discuss the validity of using a two sample t-test to compare the mean metabolic rate between trauma patients and non-trauma patients.