I am working on a problem in which I have daily Sales and daily Offline and Online Marketing Spends. I built a linear regression model where Sales = f(Online Spend, Offline Spend, Lag Sales) at rolled-up weekly level. R square from the model is 92%; however, my intercept is negative, which does not make sense as even intercept should give the unexplained sales which should be non-zero in this case.
Am I missing something here? What could be possible reasons why the model is throwing a negative intercept? Any alternative suggestion/approach is much appreciated.