Ad campaigns that appeal to emotions are more effective than rational ones at every level, according to a controversial report from the Institute of Practitioners in Advertising.

The IPA, the U.K.'s agency association, combed through 880 case studies from the past 25 years in the group's prestigious annual effectiveness awards to find out what really works.

The report, called "Marketing in the Era of Accountability," flags a dilemma for marketers: Emotional campaigns are highly effective in the long term but respond slowly to metrics such as awareness, direct-response rates and brand image. Rational, information-based campaigns track well almost immediately, but they don't ultimately deliver great business results.

"A lot of clients, especially in the U.S., are schooled in the rational U.S.P. -- finding a product difference and then using advertising to convey a message rather than build a relationship," said Les Binet, European director of DDB Matrix and the report's co-author. "They don't understand the power of emotions."

More complicated
Marketing consultant Peter Field, who worked with Mr. Binet on the report, said, "It's natural that you need something to show the boss, but you should not focus on ludicrously simplistic measures like a 5% awareness shift. You've got to be more sophisticated. There is a lot of focus on these soft indicators, but they are not reliable. You should never look at one or even two. Collectively they can be more reliable, but you need to see a shift in a lot of categories to know a campaign is working."

The report claims to prove emotional campaigns -- in particular those that work on the "fame" of the brand -- are more successful.

When IPA crunched numbers from the case studies, "fame" campaigns had a 72% chance of being effective, compared to 61% for more information-based campaigns. Similarly, fame campaigns had a 39% chance of boosting corporate profits, compared with 24% for more information-based campaigns. Mr. Binet said, "You can see clearly that the more emotional the strategy, the better it worked. People might think that adding emotions in to a rational campaign might be the answer, but pure emotion works better, even in categories that are supposedly rational, like financial services and computers. ... People go by their gut feeling first."

Marketing consultant Peter Field, who worked on the IPA report, said that simplistic measures like awareness shift are not enough to determine the effectiveness of a campaign.

In the long term, the report claims, emotional communications are the only way to increase sales. The study highlights the practical difficulties of differentiating brands by rational argument in a world where functional brand advantages are rare and short-lived. To be accepted and remembered, a brand difference must be emotionally engaging to the consumer.

On every measure
Emotionally based campaigns ultimately outperformed rationally based campaigns on every single business measure -- sales, market share, profit, penetration, loyalty and price sensitivity -- in the cases studied.

Mr. Binet and Mr. Field identified a "holy trinity" of profitability: fame, differentiation and quality perception.

For example, despite a Tropicana fruit-juice campaign that lauded the natural, unprocessed benefits of the brand, market share kept falling. A change in tactics to associate the brand with cool New York breakfasts translated to a rise in market share.

In another example, retailer Marks & Spencer struggled for years with falling profits and an increasingly dowdy image. It wasn't until the retailer created a campaign that relied heavily on the emotional appeal of a glamorous lifestyle and the showmanship of models such as Twiggy, who was an icon in the '60s, and Mick Jagger's daughter Lizzie that profits doubled and Marks & Spencer's reputation was restored.

"Rational effects are [easier] to demonstrate, but they are in conflict with what is good for business," Mr. Field said. "Marketers are pushed in the wrong direction because their No. 1 priority is accountability. The chief executive is breathing down their necks for results. ... But if marketing decisions were driven by the bottom line, then the focus would be on emotional models."