Starbucks Coffee Co. uses a data-based approach to improving the quality and customer satisfaction of its products. When survey data indicated that Starbucks needed to improve its package sealing process, an experiment was conducted to determine the factors in the bag-sealing equipment that might be affecting the ease of opening the bag without tearing the inner liner of the bag.

Source: Data extracted from L. Johnson and S. Burrows, “For Starbucks, It’s in the Bag,” Quality Progress, March 2011, pp. 17–23.

Among the factors that could affect the rating of the ability of the bag to resist tears were the viscosity, pressure, and plate gap on the bag-sealing equipment. Data were collected on 19 bags in which the plate gap was varied and stored in Starbucks . Develop a multiple regression model that uses the viscosity, pressure, and plate gap on the bag-sealing equipment to predict the tear rating of the bag. Be sure to perform a thorough residual analysis. Do you think that you need to use all three independent variables in the model? Explain.