Mortar MMM typically gathers two to three years of data when building your model. We’re often asked how old data is going to effect current estimates, since usually the state of the marketing program three years ago was not reflective of what it was today.
Idea
Most likely your business as well as your marketing strategy and activities are already quite different from three years ago, due to continuous evolution of both your business and the market
Solution
Mortar MMM uses the full historical data uploaded to define your own business' trends and seasonality, while allows you to model all the Marketing and Organic variables on a more recent timeframe to correctly measure their impact through the Date Frame you select for analysis while building your model
Suggestions:
With a Daily dataset use at least 6 to 9 months of data, with Weekly at least 9 to 12 months
If there have been huge changes in your business recently, try to set the modeling windows right after or before that to avoid confusion in the model
Experiment with different length of modeling windows to improve models' accuracy
You can see how the ROI estimate has changed over time on the “Model’s Details” tab on your dashboard.