Exam 16: Multiple Regression Model Building

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Instruction 16-6 Given below are results from the regression analysis on 40 observations where the dependent variable is the number of weeks a worker is unemployed due to a layoff (Y)and the independent variables are the age of the worker (X1),the number of years of education received (X2),the number of years at the previous job (X3),a dummy variable for marital status (X4: 1 = married,0 = otherwise),a dummy variable for head of household (X5: 1 = yes,0 = no)and a dummy variable for management position (X6: 1 = yes,0 = no). The coefficient of multiple determination (R2j)the regression model using each of the 6 variables Xj as the dependent variable and all other X variables as independent variables are,respectively,0.2628,0.1240,0.2404,0.3510,0.3342 and 0.0993. The partial results from best-subset regression are given below: Model R Square Adj. R Square Std. Error X1X5Х6 0.4568 0.4116 18.3534 \times1\times2\times5\times6 0.4697 0.4091 18.3919 \times1\times3\times5\times6 0.4691 0.4084 18.4023 \times1\times2\times3\times5\times6 0.4877 0.4123 18.3416 \times1\times2\times3\times4\times5\times6 0.4949 0.4030 18.4861 -Referring to Instruction 16-6,the model that includes X1,X2,X3,X5 and X6 should be selected using the adjusted r2 statistic.

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Instruction 16-6 Given below are results from the regression analysis on 40 observations where the dependent variable is the number of weeks a worker is unemployed due to a layoff (Y)and the independent variables are the age of the worker (X1),the number of years of education received (X2),the number of years at the previous job (X3),a dummy variable for marital status (X4: 1 = married,0 = otherwise),a dummy variable for head of household (X5: 1 = yes,0 = no)and a dummy variable for management position (X6: 1 = yes,0 = no). The coefficient of multiple determination (R2j)the regression model using each of the 6 variables Xj as the dependent variable and all other X variables as independent variables are,respectively,0.2628,0.1240,0.2404,0.3510,0.3342 and 0.0993. The partial results from best-subset regression are given below: Model R Square Adj. R Square Std. Error X1X5Х6 0.4568 0.4116 18.3534 \times1\times2\times5\times6 0.4697 0.4091 18.3919 \times1\times3\times5\times6 0.4691 0.4084 18.4023 \times1\times2\times3\times5\times6 0.4877 0.4123 18.3416 \times1\times2\times3\times4\times5\times6 0.4949 0.4030 18.4861 -Referring to Instruction 16-6,what is the value of the Mallow's Cp statistic for the model that includes X1,X5 and X6?

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Two simple regression models were used to predict a single dependent variable.Both models were highly significant,but when the two independent variables were placed in the same multiple regression model for the dependent variable,R2 did not increase substantially and the parameter estimates for the model were not significantly different from 0.This is probably an example of collinearity.

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If your data has a non-linear relationship,one transformation that may be useful is the logarithmic transformation.

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Instruction 16-6 Given below are results from the regression analysis on 40 observations where the dependent variable is the number of weeks a worker is unemployed due to a layoff (Y)and the independent variables are the age of the worker (X1),the number of years of education received (X2),the number of years at the previous job (X3),a dummy variable for marital status (X4: 1 = married,0 = otherwise),a dummy variable for head of household (X5: 1 = yes,0 = no)and a dummy variable for management position (X6: 1 = yes,0 = no). The coefficient of multiple determination (R2j)the regression model using each of the 6 variables Xj as the dependent variable and all other X variables as independent variables are,respectively,0.2628,0.1240,0.2404,0.3510,0.3342 and 0.0993. The partial results from best-subset regression are given below: Model R Square Adj. R Square Std. Error X1X5Х6 0.4568 0.4116 18.3534 \times1\times2\times5\times6 0.4697 0.4091 18.3919 \times1\times3\times5\times6 0.4691 0.4084 18.4023 \times1\times2\times3\times5\times6 0.4877 0.4123 18.3416 \times1\times2\times3\times4\times5\times6 0.4949 0.4030 18.4861 -Referring to Instruction 16-6,the variable X2 should be dropped to remove collinearity.

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For a model with 3 independent variables and data set with 75 observations,the denominator degrees of freedom for the Cook's Distance Statistic would be 70.

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Using the hat matrix elements hi to determine influential points in a multiple regression model with k independent variable and n observations,Xi is an influential point if

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Using the best-subsets approach to model building,models are being considered when their

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Instruction 16-7 What are the factors that determine the acceleration time (in sec. )from 0 to 60 kilometres per hour of a car? Data on the following variables for 171 different vehicle models were collected: Accel Time: Acceleration time in sec. Cargo Vol: Cargo volume in cu.cm. EP: Engine power KPL: Kilometres per litre SUV: 1 if the vehicle model is an SUV with Coupe as the base when SUV and Sedan are both 0 Sedan: 1 if the vehicle model is a sedan with Coupe as the base when SUV and Sedan are both 0 The coefficient of multiple determination (R2j)for the regression model using each of the five variables Xj as the dependent variable and all other X variables as independent variables are,respectively,0.7461,0.5676,0.6764,0.8582,0.6632 -Referring to Instruction 16-7,what is the value of the variance inflationary factor of Cargo Vol?

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Evaluating the influence of individual data points using a studentized deleted residual test is usually done with a one-tailed t-test.

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Instruction 16-3 In Hawaii,condemnation proceedings are under way to enable private citizens to own the property upon which their homes are built.Until recently,only estates were permitted to own land,and homeowners leased the land from the estate.In order to comply with the new law,a large Hawaiian estate wants to use regression analysis to estimate the fair market value of the land.The following model was fit to data collected for n = 20 properties,10 of which are located near a cove.Model 1: Y = β 0 + β 1X1 + β 2X2 + β 3X1X2 + β 4+ β 5X2 + ε where Y = Sale price of property in thousands of dollars X1 = Size of property in thousands of square metres X2 = 1 if property located near cove,0 if not Using the data collected for the 20 properties,the following partial output obtained from Microsoft Excel is shown: SUMMARY OUTPUT Regression Statistics Multiple R 0.985 R Square 0.970 Std. Error 9.5 Observations 20 ANOVA df SS MS F Signif F Regression 5 28324 5664 62.2 0.0001 Residual 14 1279 91 Total 19 29603 Coeff StdError t stat P-Value Intercept -32.1 35.7 -0.90 0.3834 Size 12.2 5.9 2.05 0.0594 Cove -104.3 53.5 -1.95 0.0715 Size Cove 17.0 8.5 1.99 0.0661 SizeSq -0.3 0.2 -1.28 0.2204 SizeSq -0.3 0.3 -1.13 0.2749 Note: Std.Error = Standard Error -Referring to Instruction 16-3,given a quadratic relationship between sale price (Y)and property size (X1),what test should be used to test whether the curves differ from cove and non-cove properties?

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Instruction 16-6 Given below are results from the regression analysis on 40 observations where the dependent variable is the number of weeks a worker is unemployed due to a layoff (Y)and the independent variables are the age of the worker (X1),the number of years of education received (X2),the number of years at the previous job (X3),a dummy variable for marital status (X4: 1 = married,0 = otherwise),a dummy variable for head of household (X5: 1 = yes,0 = no)and a dummy variable for management position (X6: 1 = yes,0 = no). The coefficient of multiple determination (R2j)the regression model using each of the 6 variables Xj as the dependent variable and all other X variables as independent variables are,respectively,0.2628,0.1240,0.2404,0.3510,0.3342 and 0.0993. The partial results from best-subset regression are given below: Model R Square Adj. R Square Std. Error X1X5Х6 0.4568 0.4116 18.3534 \times1\times2\times5\times6 0.4697 0.4091 18.3919 \times1\times3\times5\times6 0.4691 0.4084 18.4023 \times1\times2\times3\times5\times6 0.4877 0.4123 18.3416 \times1\times2\times3\times4\times5\times6 0.4949 0.4030 18.4861 -Referring to Instruction 16-6,the variable X4 should be dropped to remove collinearity.

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