A company's six-monthly sales figures for a five-year period are given below (in millions of dollars).
|
|
1992
|
1993
|
1994
|
1995
|
1996
|
|
Jan-June
|
1.09
|
1.10
|
1.08
|
1.04
|
1.03
|
|
July-Dec
|
1.07
|
1.06
|
1.03
|
1.01
|
0.96
|
(a) Obtain a trend estimate using a centered 2 MA smoother and compute the de-trended figures assuming an additive decomposition.
(b) Assuming the seasonality is not changing over time, calculate seasonally adjusted figures for 1996.
(c) Suppose several more years of data were available. Explain in about two sentences how the classical decomposition method could be modified to allow for seasonal effects changing over time.