A recent article (J. Conklin, "It's a Marathon, Not a Sprint," Quality Progress, June 2009, pp. 46-49) discussed a metal deposition process in which a piece of metal is placed in an acid bath and an alloy is layered on top of it. The key quality characteristic is the thickness of the alloy layer. The file Thickness contains the following variables:
Thickness-Thickness of the alloy layer
Catalyst-Catalyst concentration in the acid bath pH-pH level of the acid bath
Pressure-Pressure in the tank holding the acid bath
Temp-Temperature in the tank holding the acid bath
Voltage-Voltage applied to the tank holding the acid bath
Develop the most appropriate multiple regression model to predict the thickness of the alloy layer. Be sure to perform a thorough residual analysis. The article suggests that there is a significant interaction between the pressure and the temperature in the tank. Do you agree?