Exercise 13. 21 gave data on x = nerve firing frequency and y = pleasantness rating when nerves were stimulated by a light brushing stoke on the forearm. The x values and the corresponding residuals from a simple linear regression are as follows:

a. Construct a standardized residual plot. Does the plot exhibit any unusual features?
b. A normal probability plot of the standardized residuals follows. Based on this plot, do you think it is reasonable to assume that the error distribution is approximately normal? Explain.

Firing Frequency, x 23 24 Standardized Residual 0.04 1.45 0.20 25 27 28 34 1.19 -0.24 -0.13 -0.81 1.17 36 34 0 -1 -2 -2.0-1.51.00.5 0.0 0.5 1.0 .5 Standardized residual