The thickness of a plastic film (in mils) on a substrate material is thought to be influenced by the temperature at which the coating is applied. A completely randomized experiment is carried out. Eleven substrates are coated at 1250F, resulting in a sample mean coating thickness of and a sample standard deviation of s1 = 5.08. Another 13 substrates are coated at 1500F, for which 20.15 are observed.
It was originally suspected that raising the process temperature would reduce mean coating thickness. Do the data support this claim? Use the P-value approach and assume that the two population standard deviations are not equal.