06 - Solutions to the Mountain States Potato Company Case...

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Solutions to the Mountain States Potato Company Case 101 The Mountain States Potato Company The independent variables involved are the pH of the filter cake (PH), the pressure in the vacuum line below the fluid line on the rotating drum (LOWER), the pressure of the vacuum line above the fluid line on the rotating drum (UPPER), cake thickness measured on the drum (THICK), setting used to control the drum speed (VARIDRIV), and the speed at which the drum was rotated when collecting filter cake (DRUMSPD). These data are contained in the POTATO file. We begin our analysis of the potato processing data by first measuring the amount of collinearity that exists between the explanatory variables through the use of the variance inflationary factor. The following figure represents partial PHStat output for a multiple linear regression model in which the percent of solids is predicted from the six explanatory variables. We observe that four of the VIF are above 5.0, ranging from 9.9 for Varidriv to 8.4 for Upper. Thus, based on the criteria developed by Snee, there is evidence of collinearity among at least some of the explanatory variables. A reasonable strategy is to remove the independent variable with the largest VIF above 5, and determine what effect this has on the VIF of the remaining independent variables. Regression Analysis Regression Analysis PH and all other X Lower Pressure and all other X Regression Statistics Regression Statistics Multiple R 0.561502 Multiple R 0.939267 R Square 0.315284 R Square 0.882222 Adjusted R Square 0.243959 Adjusted R Square 0.869954 Standard Error 0.232255 Standard Error 0.716466 Observations 54 Observations 54 VIF 1.460459 VIF 8.490574 Regression Analysis Regression Analysis Upper Pressure and all other X Cake Thickness and all other X Regression Statistics Regression Statistics Multiple R 0.93823 Multiple R 0.616598 R Square 0.880276 R Square 0.380193 Adjusted R Square 0.867805 Adjusted R Square 0.31563 Standard Error 0.766658 Standard Error 0.108131 Observations 54 Observations 54 VIF 8.352558 VIF 1.613407 Regression Analysis Regression Analysis Varidriv speed and all other X Drum speed setting and all other X Regression Statistics Regression Statistics Multiple R 0.948243 Multiple R 0.946259 R Square 0.899165 R Square 0.895406 Adjusted R Square 0.888661 Adjusted R Square 0.884511 Standard Error 0.179475 Standard Error 2.150324 Observations 54 Observations 54 VIF 9.917201 VIF 9.560793 Figure 1 Regression Model obtained from PHStat to Predict Percent of Solids based on Six Explanatory Variables
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102 Solutions to the Mountain States Potato Company Case The following figure represents the regression model obtained from PHStat with only the Varidriv variable removed from the model. Regression Analysis
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This homework help was uploaded on 04/09/2008 for the course ENGR, STAT 320, 262, taught by Professor Harris during the Spring '08 term at Purdue.

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06 - Solutions to the Mountain States Potato Company Case...

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