Exam 15: Multiple Regression Model Building

SCENARIO 15-2 In Hawaii, condemnation proceedings are under way to enable private citizens to own the property that their homes are built on.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: where Y Sale price of property in thousands of dollars Size of property in thousands of square feet 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 -Referring to Scenario 15-2, given a quadratic relationship between sale price (Y)and property size , what test should be used to test whether the curves differ from cove and non-cove properties?

SCENARIO 15-5 What are the factors that determine the acceleration time (in sec.)from 0 to 60 miles 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.ft. HP: Horsepower MPG: Miles per gallon 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 ( )for the regression model using each of the 5 variables 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 Scenario 15-5, what is the value of the variance inflationary factor of HP?

SCENARIO 15-3 A chemist employed by a pharmaceutical firm has developed a muscle relaxant.She took a sample of 14 people suffering from extreme muscle constriction.She gave each a vial containing a dose (X)of the drug and recorded the time to relief (Y)measured in seconds for each.She fit a curvilinear model to this data.The results obtained by Microsoft Excel follow SUMMARY OUTPUT -Referring to Scenario 15-3, suppose the chemist decides to use a t test to determine if there is a significant difference between a linear model and a curvilinear model that includes a linear term.If she used a level of significance of 0.01, she would decide that the linear model is sufficient.

SCENARIO 15-6 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 ( ), the number of years of education received ( ), the number of years at the previous job ( ), a dummy variable for marital status ( 1 = married, 0 = otherwise), a dummy variable for head of household ( 1 = yes, 0 = no)and a dummy variable for management position ( 1 = yes, 0 = no). The coefficient of multiple determination ( )for the regression model using each of the 6 variables 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: -Referring to Scenario 15-6, the model that includes all the six independent variables should be among the appropriate models using the Mallow's statistic.

SCENARIO 15-6 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 ( ), the number of years of education received ( ), the number of years at the previous job ( ), a dummy variable for marital status ( 1 = married, 0 = otherwise), a dummy variable for head of household ( 1 = yes, 0 = no)and a dummy variable for management position ( 1 = yes, 0 = no). The coefficient of multiple determination ( )for the regression model using each of the 6 variables 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: -Referring to Scenario 15-6, the model that includes should be selected using the adjusted statistic.

SCENARIO 15-3 A chemist employed by a pharmaceutical firm has developed a muscle relaxant.She took a sample of 14 people suffering from extreme muscle constriction.She gave each a vial containing a dose (X)of the drug and recorded the time to relief (Y)measured in seconds for each.She fit a curvilinear model to this data.The results obtained by Microsoft Excel follow SUMMARY OUTPUT -Referring to Scenario 15-3, suppose the chemist decides to use an F test to determine if there is a significant curvilinear relationship between time and dose.If she chooses to use a level of significance of 0.05, she would decide that there is a significant curvilinear relationship.

Which of the following will NOT change a nonlinear model into a linear model?

SCENARIO 15-6 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 ( ), the number of years of education received ( ), the number of years at the previous job ( ), a dummy variable for marital status ( 1 = married, 0 = otherwise), a dummy variable for head of household ( 1 = yes, 0 = no)and a dummy variable for management position ( 1 = yes, 0 = no). The coefficient of multiple determination ( )for the regression model using each of the 6 variables 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: -Referring to Scenario 15-6, the variable x₂ should be dropped to remove collinearity?

One of the consequences of collinearity in multiple regression is biased estimates on the slope coefficients.

Which of the following is used to find a "best" model?

SCENARIO 15-6 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 ( ), the number of years of education received ( ), the number of years at the previous job ( ), a dummy variable for marital status ( 1 = married, 0 = otherwise), a dummy variable for head of household ( 1 = yes, 0 = no)and a dummy variable for management position ( 1 = yes, 0 = no). The coefficient of multiple determination ( )for the regression model using each of the 6 variables 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: -Referring to Scenario 15-6, what is the value of the variance inflationary factor of Edu?

SCENARIO 15-6 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 ( ), the number of years of education received ( ), the number of years at the previous job ( ), a dummy variable for marital status ( 1 = married, 0 = otherwise), a dummy variable for head of household ( 1 = yes, 0 = no)and a dummy variable for management position ( 1 = yes, 0 = no). The coefficient of multiple determination ( )for the regression model using each of the 6 variables 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: -Referring to Scenario 15-6, there is reason to suspect collinearity between some pairs of predictors based on the values of the variance inflationary factor.

SCENARIO 15-5 What are the factors that determine the acceleration time (in sec.)from 0 to 60 miles 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.ft. HP: Horsepower MPG: Miles per gallon 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 ( )for the regression model using each of the 5 variables 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 Scenario 15-5, what is the value of the variance inflationary factor of Sedan?

SCENARIO 15-4 The superintendent of a school district wanted to predict the percentage of students passing a sixth-grade proficiency test.She obtained the data on percentage of students passing the proficiency test (% Passing), daily mean of the percentage of students attending class (% Attendance), mean teacher salary in dollars (Salaries), and instructional spending per pupil in dollars (Spending)of 47 schools in the state. Let Y = % Passing as the dependent variable, Attendance, Salaries and Spending. The coefficient of multiple determination ( )of each of the 3 predictors with all the other remaining predictors are, respectively, 0.0338, 0.4669, and 0.4743. The output from the best-subset regressions is given below: Following is the residual plot for % Attendance: Following is the output of several multiple regression models: -Referring to Scenario 15-4, the null hypothesis should be rejected when testing whether the quadratic effect of daily average of the percentage of students attending class on percentage of students passing the proficiency test is significant at a 5% level of significance.

SCENARIO 15-1 A certain type of rare gem serves as a status symbol for many of its owners.In theory, for low prices, the demand increases, and it decreases as the price of the gem increases.However, experts hypothesize that when the gem is valued at very high prices, the demand increases with price due to the status owners believe they gain in obtaining the gem.Thus, the model proposed to best explain the demand for the gem by its price is the quadratic model: where Y = demand (in thousands)and X = retail price per carat. This model was fit to data collected for a sample of 12 rare gems of this type.A portion of the computer analysis obtained from Microsoft Excel is shown below: SUMMARY OUTPUT -Referring to Scenario 15-1, does there appear to be significant upward curvature in the response curve relating the demand (Y)and the price (X)at 10% level of significance?

SCENARIO 15-3 A chemist employed by a pharmaceutical firm has developed a muscle relaxant.She took a sample of 14 people suffering from extreme muscle constriction.She gave each a vial containing a dose (X)of the drug and recorded the time to relief (Y)measured in seconds for each.She fit a curvilinear model to this data.The results obtained by Microsoft Excel follow SUMMARY OUTPUT -Referring to Scenario 15-3, suppose the chemist decides to use an F test to determine if there is a significant curvilinear relationship between time and dose.The value of the test statistic is ________.

SCENARIO 15-4 The superintendent of a school district wanted to predict the percentage of students passing a sixth-grade proficiency test.She obtained the data on percentage of students passing the proficiency test (% Passing), daily mean of the percentage of students attending class (% Attendance), mean teacher salary in dollars (Salaries), and instructional spending per pupil in dollars (Spending)of 47 schools in the state. Let Y = % Passing as the dependent variable, Attendance, Salaries and Spending. The coefficient of multiple determination ( )of each of the 3 predictors with all the other remaining predictors are, respectively, 0.0338, 0.4669, and 0.4743. The output from the best-subset regressions is given below: Following is the residual plot for % Attendance: Following is the output of several multiple regression models: -Referring to Scenario 15-4, which of the following predictors should first be dropped to remove collinearity?

So that we can fit curves as well as lines by regression, we often use mathematical manipulations for converting one variable into a different form.These manipulations are called dummy variables.

SCENARIO 15-3 A chemist employed by a pharmaceutical firm has developed a muscle relaxant.She took a sample of 14 people suffering from extreme muscle constriction.She gave each a vial containing a dose (X)of the drug and recorded the time to relief (Y)measured in seconds for each.She fit a curvilinear model to this data.The results obtained by Microsoft Excel follow SUMMARY OUTPUT -Referring to Scenario 15-3, suppose the chemist decides to use an F test to determine if there is a significant curvilinear relationship between time and dose.If she chooses to use a level of significance of 0.01 she would decide that there is a significant curvilinear relationship.

SCENARIO 15-4 The superintendent of a school district wanted to predict the percentage of students passing a sixth-grade proficiency test.She obtained the data on percentage of students passing the proficiency test (% Passing), daily mean of the percentage of students attending class (% Attendance), mean teacher salary in dollars (Salaries), and instructional spending per pupil in dollars (Spending)of 47 schools in the state. Let Y = % Passing as the dependent variable, Attendance, Salaries and Spending. The coefficient of multiple determination ( )of each of the 3 predictors with all the other remaining predictors are, respectively, 0.0338, 0.4669, and 0.4743. The output from the best-subset regressions is given below: Following is the residual plot for % Attendance: Following is the output of several multiple regression models: -Referring to Scenario 15-4, the quadratic effect of daily average of the percentage of students attending class on percentage of students passing the proficiency test is not significant at a 5% level of significance.