Table 3.4 showed data on accidents involving trains. a. Is it plausible that the collision counts are independent Poisson variates with constant rate over the 29 years? Respond by comparing a Poisson...

Table 3.4 showed data on accidents involving trains.

a. Is it plausible that the collision counts are independent Poisson variates with constant rate over the 29 years? Respond by comparing a Poisson GLM for collision rates that contains only an intercept term to a Poisson GLM that contains also a time trend. The deviances of the two models are 35.1 and 23.5.

b. Section 3.3.6 fitted a negative binomial model. The estimated collision rate x years after 1975 was
The

c. The likelihood-ratio 95% confidence interval for β is (−0.060, −0.008). Find the interval for the multiplicative annual effect on the accident rate, and interpret.