11.5

(a) Using the data of Problem 11.1, fit a regression line through the data, using t and t 2 as explanatory variables (t is a time trend 1–36). Use only the observations from 2000–2006. Calculate the trend values using the regression.

(b) Calculate the seasonal factors (multiplicative model) based upon this trend. How do they compare to the values found in Problem 11.1?

(c) Predict the value of consumers’ expenditure for 2007 Q4.

(d) Calculate the seasonal factors using the additive model and predict consumers’ expenditure for 2007 Q4.