The next table presents the quarterly sales index for one brand of graphing calculator at a campus

Question:

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:

if Quarter 1 lo otherwise S1 if Quarter 2 Qi Q2= otherwise Si if Quarter 3 Q3 lo otherwise 이U 이니 이니.
Second Quarter First Fourth Quarter Third Quarter Year Quarter 2011 2012 2013 2014 2015 438 464 523 593 636 398 429 496

a. Write a regression model for E(Yt) as a function of t, Q1, Q2, and Q3.
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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Related Book For  book-img-for-question

Statistics For Business And Economics

ISBN: 9780134506593

13th Edition

Authors: James T. McClave, P. George Benson, Terry Sincich

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