The State Tax Commission must download information files each morning. The time to download the files primarily depends on the size of the file. The Tax Commission has asked your computer consulting firm to determine what, if any, relationship exists between download time and size of files. The Tax Commission randomly selected a sample of days and provided the information contained in the file Tax Commission.
a. Develop a scatter plot of the data with the dependent variable, download time, on the vertical axis and the independent variable, size, on the horizontal axis. Does there appear to be a relationship between the two variables? Is the relationship linear?
b. Compute the sample correlation coefficient between the two variables. Conduct a test, using an alpha value of 0.05, to determine whether the population correlation coefficient is significantly different from zero.
c. Determine the simple linear regression model for these data. Plot the simple linear regression model together with the data. Would a nonlinear model better fit the sample data?
d. Now determine a nonlinear model and plot the model against the data. Does the nonlinear model provide a better fit than the linear model developed in part c?