In: Statistics and Probability
We are trying to maximise the lifetime of a particular engine by testing two different types of maintenance schedule. We test Schedule A on 40 engines which leads to an average lifetime of 13.2 years with a standard deviation of 3.1. We test Schedule B on another 40 engines which leads to an average lifetime of 10.4 years with a standard deviation of 2.1. The 98.5% confidence interval for the difference in the lifetimes is given by: