“What impact did our Black Friday promo really have on revenue?” It’s one of the most common questions we hear from our clients, and it’s why we built one of our favorite features at Recast: Spike Modeling. Traditionally, MMMs have tried to capture the effects of holiday sales using dummy variables. A dummy variable is a simple switch in the model—turning “on” for a holiday like Black Friday and “off” for the rest of the year. While this approach might seem logical, it’s deeply flawed.  Dummy variables: Overcredit sales to the holiday event itself without accounting for the impact of marketing. Fail to account for consumer behaviors like delaying purchases until a sale (pull-forward effects) or stockpiling during the sale…