# Consider the following time series representing natural gas

Question 1:

Consider the following time series representing Natural Gas Sales for Northern Natural Gas Company for the years 2007-2010.

See printscreen with question 1 data

Use this information to answer (a) through (f). Type your answers in the box below.

(a) Interpret the value of S3, the seasonal index in the third quarter. That is, how much higher or lower are natural gas sales in the third quarter compared to the base (trend) line?

(b) Calculate d9, the deseasonalized value for the 1st quarter of 2009 (t = 9).

(c) State which of the columns in the above table (choose from either Year, Quarter, t, Yt, St, dt, or Tt) would be used as the X and the Y variables in a regression analysis that would determine the trend component? Be sure to state which column is the X (independent) and which is the Y (dependent).

(d) Assuming the trend line can be described as Tt = 152.79 – 1.12*t, forecast the value of the trend component for the first quarter of 2011 (t = 17).

(e) What is the seasonal component for the first quarter of 2011 (t = 17)?

(f) Calculate the seasonally adjusted forecast for the first quarter of 2011 (t = 17).

Question 2:

Consider the following time series representing the weekly number of computers sold for the last 16 weeks, also shown in the Excel file bus305exam3data-S11.xlsx under Data Set A. Also shown are the Simple Exponential Smoothing (SES) forecasts using a smoothing constant (alpha) of 0.3.

Use this information to answer (a) and (b). Type your responses in the box below.

(a) What is the value of F1, the SES forecast for t = 1?

(b) What is the forecasted value for week 17 (again, using Simple Exponential Smoothing with alpha = 0.3)?

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