Concept explainers
Graphing calculator sales. The next table presents the quarterly sales index for one brand of graphing calculator at a campus bookstore. The quarters are based on an academic year, so the first quarter represents fall; the second, winter; the third, spring; and the fourth, summer. Define the time variable as t = 1 for the first quarter of 2011, t = 2 for the second quarter of 2011, etc. Consider the following seasonal dummy variables:
a. Write a regression model for E (Yt) as a
b. Find and interpret the least squares estimates and evaluate the usefulness of the model.
c. Which of the assumptions about the random error component is in doubt when a regression model is fit to time series data?
d. Find the forecasts and the 95% prediction intervals for the 2016 quarterly sales. Interpret the result.
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Statistics Sta 2122 Second Custom Edition For Florida International University
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