APA Dictionary of Psychology

a method of testing advertising effectiveness in a printed medium, such as a magazine or newspaper, by inducing the reader to return a coupon by mail. The technique is sometimes used on a split-run basis in which the coupon is offered only to one part of the publication’s readership; alternatively, variations of an advertisement may be tested in different demographic areas in which the publication is sold. Some publications cooperate with advertisers using the coupon-return technique by charging for advertising space on a per-inquiry (p.i.) basis, each coupon returned counting as an inquiry.