I have to do forecasting of sales that is how much sales of a product is going to happen in a particular store. I have time series data for last two years and doing forecasting for 2014. The variables are promotion flag ( Yes/ No ), promotion period, location in a store, price discount. These all are categorical variables.
For this I am using regression method where, dependent variable is sales, and independent variables are categorical variables mentioned above. This analysis is done in SPSS where I have used step-wise and backward regression.
Below is the link for the data:
I want to know, the regression model is under-forecasting? Is there a way to improve the forecast?