Question

A polymer is manufactured in a batch chemical process. Viscosity measurements are normally made on each batch, and long experience with the process has indicated that the variability in the process is fairly stable with σ = 20. Fifteen batch viscosity measurements are given as follows: 724, 718, 776, 760, 745, 759, 795, 756, 742, 740, 761, 749, 739, 747, 742. A process change that involves switching the type of catalyst used in the process is made. Following the process change, eight batch viscosity measurements are taken: 735, 775, 729, 755, 783, 760, 738, 780.

a. If µ₁ - µ₂ is the mean batch viscosity before and after the process change, can you conclude that µ₁ - µ₂ is less than 10 at 0.10 level of significance? Use the confidence interval method – that is, the solution will include a confidence interval, a final conclusion and an explanation for how this interval is used to draw your conclusion.

b. Is your method used in part (a) justified? If not, do you need any additional assumptions?

Answer 1