The incremental reach for an ad in an advertising campaign is the amount that the reach for the entire campaign would decline if that one ad was removed from the campaign.
The figure below shows an 8 week luxury car advertising campaign, sorted by incremental reach. The campaign includes a total of 452 ads on 4 broadcast networks and 27 cable networks.
It indicates that if the first ad in the list, a Sunday sports ad on Fox, would have been dropped from the campaign, then the total
for the campaign would decline by 1.91. Note that the program had a 12.9 rating, so about 15% of the audience for this ad was new to the ad campaign. This is defined as the ad change ratio. It is the portion of the audience for the ad that was unique to the campaign.