The Chevy Tahoe Hybrid got a lot of attention when it first appeared. It is a relatively high-priced hybrid SUV that makes use of the latest technologies for fuel efficiency. One of the more popular hybrid SUVs on the market is the modestly priced Ford Escape Hybrid. A consumer group was interested in comparing the gas mileage of these two models. In order to do so, each vehicle was driven on the same 10 routes that combined both highway and city streets. The results showed that the mean mileage for the Chevy Tahoe was 29 mpg and for the Ford Escape it was 31 mpg. The standard deviations were 3.2 mpg and 2.5 mpg, respectively.
a) An analyst for the consumer group computed the two-sample t 95% confidence interval for the difference between the two means as 1 -0.71, 4.712. What conclusion would he reach based on this analysis?
b) Why is this procedure inappropriate? What assumption is violated?
c) In what way do you think this may have impacted the results?