Question 11.21

11.21 Predicting the price of tablets: Multiple regression equation.

Refer to the tablet data described in Exercise 11.19.

tablts

  1. Run a multiple regression to predict price using the six product characteristics. Give the equation for predicted price.
  2. What is the value of the regression standard error ? Verify that this value is the square root of the sum of squares of residuals divided by the degrees of freedom for the residuals.
  3. Obtain the residuals and use graphical summaries to describe the distribution.
  4. Observation 11 is much higher priced than the model predicts. Remove this observation and repeat parts (a), (b), and (c). Comment on the differences between the two model fits.

11.21

(a)
. (b) . (c) A Normal quantile plot shows a potential outlier. (d)
.
A Normal quantile plot shows the residuals are much closer to a Normal distribution without the outlier; however, there still appears to be slightly heavy tails. This model is likely much better than the original model. Before only Size was significant, now Battery and Display are significant at the 5% level; the standard error is much smaller for the second model as well.