The “spillover” or indirect sales effect from a publisher’s performance marketing / direct response advertising campaigns.
Various studies have shown that in addition to the traceable orders, company’s performance marketing promotions produce indirect and untraceable sales, called echo, through all of the other outlets where products are normally sold.
A test to establish the spillover or indirect ordering resulting from a promotion effort is recommended. Virtually all promotions aimed at direct response produce an echo sales effect which may be anywhere from 1 to 20 times as great as the traceable direct response, depending on product, price, audience, and timing.
A conservative estimate is of 1.5 echo orders for each direct order of a book as a rule-of-thumb, although in one echo study, a mailing that brought in no direct responses resulted in total sales 17 times greater in the period following the mailing compared with a similar period prior to the mailing.