That's one of the major findings from "Adworks2," a two-year study of more than 800 package-goods brands conducted by Media Marketing Assessment, a unit of Carat USA, in conjunction with Information Resources Inc.'s Infoscan and Nielsen Media Research's Monitor-Plus.
Using a scale of 100% representing average sales per TV impression, if a marketer puts 6% to 50% of its TV plan into 30-second commercials, the resulting sales per impression index averages 71%.
SALES PER IMPRESSION
But if a marketer puts 81% to 99% of its plan into :30s, the index jumps to 96% sales per impression. And if a marketer uses all :30s and no :15s, the payoff indexes at 140% sales per impression.
"There does seem to be a significant trade-off in the use of :15s," said David Poltrack, exec VP-planning and research for CBS-TV. CBS, along with ABC, NBC, Fox, Nabisco Foods, Kraft Foods and Hershey Foods Corp. helped fund the study.
"To the extent you are using :15s, you are paying less money," noted Mr. Poltrack. "Usually the going rate for :15s is 60% to 65% of :30s. But it's probably not cost-effective to use a lot of :15s in your campaign."
Erwin Ephron, media consultant at Ephron Papazian Ephron, said that :15s "need to be discounted by marketers, but they are reluctant to do so." One reason 15-second spots are so attractive, Mr. Ephron said, is the high cost of TV advertising.
Another finding that some might find surprising is that product discounting or couponing can decrease the effectiveness of TV ads.
"When you put out a 50 cent coupon or discount your product 20%, the predominant buyers are your current customers," Mr. Poltrack explained. "The marketer hopes he will get new customers that will offset the revenue loss. So with the discounting or couponing, consumers buy more than their normal supply of the product. Thus in the next buying cycle, they aren't buying. So as your TV advertising goes on, it's in a market of lower demand."
What makes the study most valuable to the networks is its endorsement of the effectiveness of network TV in particular. Currently, on average, national advertisers put 35% of their gross ratings points into cable TV shows.
But according to "Adworks2," the most effective ad schedules, from a sales-per-TV-impression point of view, were ones that used a mix of about 24% of GRPs in network prime-time; about 31% in network daytime; about 31% in cable (all dayparts); with the rest in a mix of spot and syndication.
The first study was conducted in 1995 and 1996, and the TV landscape has changed since then. There is more clutter, and cable, collectively, delivers a larger audience now; the networks a smaller one.
However, "The universality of the results suggests that those changes are not in themselves substantial enough to affect the overall conclusions of the study," Mr. Poltrack said. "The point is that for every brand studied -- new, established, large or small -- TV advertising worked."