A regional express delivery service company recently conducted a study to investigate the relationship between the cost of shipping a package (Y), the package weight (X1), and the distance shipped (X2). Twenty packages were randomly selected from among the large number received for shipment, and a detailed analysis of the shipping cost was conducted for each package. These sample observations are given in the file P10_22.xlsx.
a. Estimate a simple linear regression equation involving shipping cost and package weight. Interpret the slope coefficient of the least squares line and the R2 value.
b. Add another explanatory variable, distance shipped, to the regression model in part a. Estimate and interpret this expanded equation. How does the R2 value for this multiple regression equation compare to that of the simple regression equation in part a? Explain any difference between the two R2 values. Interpret the adjusted R2 value for the revised equation.