Hawaii tourism, part 4.

In Exercise 40, we fit a linear regression for the number of monthly international visitors to Hawaii (for the years 2002 through 2006) using Time and dummy variables for the months as predictors.

The R2 value was 59.9% and a residual plot against Time would show a few low outliers, but no discernible pattern.
The dataset for this exercise contains the same data for the period January 2000 through May 2013.

a) Fit the linear model from Exercise 40 to this entire time period.

b) Is the trend term statistically significant?

c) Would you use this model? Explain.

d) Why does the no trend model from Exercise 40 no longer work?