The inventory manager at a warehouse distributor wants to predict inventory cost (Cost in $) based on order quantity (Quantity in units). She thinks it may be a nonlinear relationship because its two primary components move in opposite directions: (1) order processing cost (costs of procurement personnel, shipping, transportation), which decreases as order quantity increases (due to fewer orders needed), and (2) holding cost (costs of capital, facility, warehouse personnel, equipment), which increases as order quantity increases (due to more inventory held). She has collected monthly inventory costs and order quantities for the past 36 months. A portion of the data is shown in the accompanying table.

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The inventory manager at a warehouse distributor wants to predict inventory cost (Cost in $) based on order quantity (Quantity in units). She thinks it may be a nonlinear relationship because its two primary components move in opposite directions: (1) order processing cost (costs of procurement personnel, shipping, transportation), which decreases as order quantity increases (due to fewer orders needed), and (2) holding cost (costs of capital, facility, warehouse personnel, equipment), which increases as order quantity increases (due to more inventory held). She has collected monthly inventory costs and order quantities for the past 36 months. A portion of the data is shown in the accompanying table. 

Cost Quantity
54.4 844
52.1 503
60.2 300
53.8 869
51.7 525
57.1 1030
61.1 288
49.8 577
53.9 490
48.2 588
47.5 606
57.4 325
59.6 1160
58.2 1072
58.7 308
58.1 1140
48.4 627
63.4 214
62.5 207
62.5 1174
62.7 1190
61.2 1166
55.9 1067
51.3 655
57.1 384
58.2 367
55.8 927
54.9 890
54.7 495
50.2 780
60.8 1168
54.8 403
51.3 741
51.9 712
49.8 612
55.5 870

 

a.  Estimate the linear regression model to predict inventory cost as a function of order quantity. Then estimate the quadratic regression model to predict inventory cost as a function of order quantity and order quantity squared. (Negative values should be indicated by a minus sign. Round your answers to 2 decimal places.)

Cost = 54.43  +     0.01 Quantity

Cost =  74.64 +    -0.07  Quantity +  0.00     Quanity (squared)

 

b-1. Evaluate the linear model in terms of variable significance (α = 0.05) and adjusted R2.

The adjusted R squared is negative and the explanatory variable  is not significant

 

b-2. Evaluate the quadratic model in terms of variable significance (α = 0.05) and adjusted R2(Round your answer to 2 decimal places.)

 

The adjusted R squared is 0.86 % and the explanatory variables are significant

 

 

b3. Use the best-fitting model to predict monthly inventory cost for an order quantity of 800 units. (Do not round the estimates or intermediate calculations. Round your final answer to 2 decimal places.)

 

The linear or quadratic model is best providing a predicted value of ___?___ cost.

 

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