Refer to the plot of residuals in Figure 14.13 for Exercise 14.6.

(a) Explain why a more valid fit may result from assuming that income has a gamma distribution, rather than a normal distribution.

(b) Table 14.11 shows results for the normalGLMand the gamma GLM. Summarize how results differ for the two models.

(c) Interpret the scale parameter estimate by estimating the standard deviation of income when its conditional mean is (i) $20,000 (ii) $50,000.