Lift is promoted sales minus the baseline, expressed in units and as a ratio to the baseline. It is the number that decides whether a promotion paid for itself: the margin earned on the incremental units, against the cost of the funding, the allowances and the reduced price given on the units that would have sold anyway.
Gross lift overstates the effect. Some of the extra units were taken from the shopper’s own later purchases — stock bought on promotion and used in the weeks after — and some from the manufacturer’s other products, or from the same product in neighboring weeks and stores. Net incremental units, after those offsets and with any halo on related products added back, is the figure a promotion’s return should be judged on.
Lift measured on the retailer’s scan data and lift implied by the manufacturer’s shipments rarely agree, because shipments include stock bought for the event that has not yet sold. Measuring on consumer sales is what keeps a forward-buy from being counted as a success.