Consider the following quarterly demand levels for electricity (in 1 000 megawatts) in Cape Town from 2008 to 2011.
|
Months
|
2008
|
2009
|
2010
|
2011
|
|
Jan-Mar
|
21
|
35
|
39
|
78
|
|
Apr-Jun
|
42
|
54
|
82
|
114
|
|
Jul-Sep
|
60
|
91
|
136
|
160
|
|
Oct-Dec
|
12
|
14
|
28
|
40
|
(a) Plot the time series of quarterly electricity demand graphically.
(b) Find the least squares trendline for quarterly electricity demand in Cape Town.
(c) Find the seasonal index for each quarter.
(d) Estimate the seasonally adjusted trend values of quarterly electricity demand for quarters 3 and 4 of 2012.
Excel tasks
(e) Use the Insert > Chart tab (line with markers) to plot the time series data in (a).
(f) Use the Add Trendline option (by right clicking on any data value in the line graph) to compute the least squares trendline for electricity demand in (b).