a. Construct a time-series graph of the sales data for HeathCo’s line of skiwear. Does there appear to be a seasonal pattern in the sales data? Explain why you think the results are as you have found.

b. It seems logical that skiwear would sell better from October through March than from April through September. To test this hypothesis, begin by adding two dummy variables to the data: a dummy variable Q1 = 1 for each first quarter (January, February, March) and Q1 = 0 otherwise; and a dummy variable Q4 = 1 for each fourth quarter (October, November, December) and Q4 = 0 otherwise. Once the dummy variables have been entered into your data set, estimate the following trend model:

c. Prepare a time-series plot of SALES (for 2007Q1 through 2016Q4) along with SF2 (for 2017Q1 through 2017Q4) to illustrate how SALES and SF2 compare.