Suppose the Human Resources director at NVR, a large construction company, believes that the number of sick hours per year taken by an employee is related to the commuting distance. A random sample of employees was obtained, and each person’s travel distance to work (x, in miles) was recorded. Personnel records were used to obtain the number of hours off for sickness in a year (y) for each employee included in the study.
a. Find the estimated regression line, and compute the residuals.
b. Conduct an F test for a significant regression. Use a significance level of 0.10. Do you believe that there is a relationship between commuting distance and sick hours? Why or why not?
c. Carefully sketch a normal probability plot of the residuals and a plot of the residuals versus the predictor variable.
d. Do these graphs provide any evidence that the simple linear regression assumptions are invalid? Justify your answer.
Researchers at a marine institute investigated the relationship between the dissolved barium concentration and the silicate/nitrate ratio in the North Pacific Ocean. The silicate/nitrate ratio (x) and the dissolved barium concentration (y, in nmol/kg) were measured at randomly selected locations. NPOCEAn
a. Find the estimated regression line, and compute the residuals.
b. Conduct an F test for a significant regression. Use a significance level of 0.01.
c. Carefully sketch a normal probability plot of the residuals and a plot of the residuals versus the predictor variable.
d. Do these graphs provide any evidence that the simple linear regression assumptions are invalid? Justify your answer.