For years, advertising agencies have been coaxing people into back rooms at malls to review ads in exchange for a couple of dollars or a lotto ticket. Although this method of gauging ad effectiveness is useful for gathering thoughts about whether an advertisement is liked or disliked by a reader, it doesn't convey the whole story to the ad agency. Marketers want to know things like: Did you read the copy first or look at the photo? Are you distracted by a particular color? How obvious is the risk information? Does this ad have stopping power? Plus, with the mall approach, agencies must factor in the reality that many focus group participants just give the answers marketers want to hear and collect their cash.