Exercise 5-29 presented measurements of plastic coating thickness at two different application…


Exercise 5-29 presented measurements of plastic coating thickness at two different application temperatures. Test the appropriate hypothesis to demonstrate that the variance of the thickness is less for the 125°F process than the 150F process, using α = 0.10.

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Exercise 5-29

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 125°F, resulting in a sample mean coating thickness of  1 = 101.28 and a sample standard deviation of s1 = 5.08. Another 13 substrates are coated at 150°F, for which 2 = 101.70 and s2 = 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.