The potentially deadly 2009 Swine Flu outbreak was due to a new flu strain o f subtype H1N1 not previously reported in pigs. When the W orld Health Organization declared a pandemic, the virus continued to spread in the United States, causing illness along w ith regular seasonal influenza viruses. Consider the follow ing 2009 weekly data on total Swine Flu cases in the United States, reported by the Centers for Disease Control and Prevention (CDC).

Week Total Week Total 17 1,190 22 2,904 18 2,012 23 3,024 19 1,459 24 3,206 20 2,247 25 1,829 21 2,280 26 1,093 SOURCE: w w w .c d c .g o v .

a. Plot the series. Estimate the linear and the quadratic trend models. Use their adjusted R2to choose the preferred model.

b. Given the preferred model, make a forecast for the number of Swine Flu cases in the U.S. for week 27.