In: Statistics and Probability
Two catalysts in a batch chemical process, are being compared for their effect on the output of the process reaction. A sample of 12 batches was prepared using catalyst 1, and a sample of 10 batches was prepared using catalyst 2. The 12 batches for which catalyst 1 was used in the reaction gave an average yield of 85 with a sample standard deviation of 4, and the 10 batches for which catalyst 2 was used gave an average yield of 81 and a sample standard deviation of 5.
(1) Find a 90% confidence interval for the difference between the population means, assuming that the populations are approximately normally distributed with equal variances.
(2) Explain with the available sample information why the assumption of equal variances is reasonable.