I have sales data for last four year. I want to divide my data in two parts so that I can have base volume and promotional volume. I am thinking to use " Decomposition of Time Series " approach such that the base volume would be trend component and seasonal and error component would be promotional volume.
Is this method would be good? Is there any other method/way to break down the data in two parts.
P.S : promotional volume is the volume that comes from promotions during festival seasons.