# Question: The following data represent more extended measurements of monthly water

The following data represent more extended measurements of monthly water usage at the plant referred to in Exercise 14.98 over a period of 20 months:

(a) Use an appropriate computer program to fit a linear surface to these data.

(b) Use a computer program to make a normal-scores plot of the residuals. Does the assumption of normality appear to be satisfied at least approximately?

(c) Plot the residuals against and determine whether the pattern is random.

(d) Check for excessive multicollinearity among the independent variables.

(a) Use an appropriate computer program to fit a linear surface to these data.

(b) Use a computer program to make a normal-scores plot of the residuals. Does the assumption of normality appear to be satisfied at least approximately?

(c) Plot the residuals against and determine whether the pattern is random.

(d) Check for excessive multicollinearity among the independent variables.

## Answer to relevant Questions

Using the data of Exercise 14.99, In exercise (a) Create a new variable, x22. (b) Fit a surface of the form (c) Find the correlation matrix of the three independent variables. Is there evidence of multicollinearity? (d) ...Solve the normal equations on page 390 simultaneously to show that Under the assumptions of normal regression analysis, show that (a) The least squares estimate of a in Theorem 14.2 can be written in the form (b) A has a normal distribution with Use the formula for t of Exercise 14.28 to derive the following (1 – α) 100% confidence limits for β: In exercise Given the joint density Show that µY|x = 1 + 1/x and that var(Y|x) does not exist.Post your question