Objective: Obtain incremental sales during promotional period
- Replace sales values during promotion periods with NA.
stl()to decompose sales into trend, season, remainder
- Forecast (trend - season) through NAs
- Add seasonal component back onto the forecasted trend. This is the base.
- The difference between the base and the actual sales is the incremental dollars due to the promotion.
Problem: Most of the actual sales, at least in my data, are lower than the base sales.
Question:I am looking for some kind of alternative method or error in my current method as I find it hard to believe that promotions have negative incremental dollars.
This is a revisit the conversation I was reading here.