Baseline conversions, in attribution, refers to the estimated number of conversions that would have happened even without any of the marketing activity being measured by the attribution model. For example, baseline conversions may have been caused by external factors such as hard-to-measure word-of-mouth marketing, or by offline advertising — which cannot be measured by attribution models.
By establishing the baseline conversions before running attribution, the marketer is able to more precisely calculate the lift provided by their marketing initiatives, and only allocate the incremental conversions to the addressable initiatives being analyzed by the attribution system
