You buy more salad dressing from Paul Newman under his own label than you would if he were in commercials for someone else, research says.

Endorsements by the rich and famous have long been a staple of the advertising industry. They can give otherwise mundane products, like razors or carpet cleaners, new cachet. Market research has shown repeatedly that celebrities can "instantly" add personality and appeal to even unknown products and make or break recognized brands.

But celebrity entrepreneurs can sell their own products better than those stars who simply endorse those of other companies, according to business analysts writing in this month's issue of International Journal of Entrepreneurship and Small Business. Those celebs are not only more heavily involved in their own products and so have a vested interest in sales, but their direct connection to the product makes them more effective in communicating why you, the consumer, should buy it.

Erik Hunter of Jönköping International Business School in Sweden working with Per Davidsson of the Brisbane Graduate School of Business, Australia, have carried out the first analysis of the marketing of celebrity products and have found that a celebrity's own involvement in the product is truly the key to its success compared with the old-style endorsement marketing.

They add that from the consumer's perspective, the celebrity's involvement in their product essentially rubs off and adds to the value of the product compared with a product being endorsed but not celebrity branded.

There are four main groups who will benefit from Hunter and Davidsson's detailed analysis. First the celebrity entrepreneurs themselves who can find out whether or not being fully involved in a product is a more effective use of their "celebrity capital" rather than simply being paid to endorse an independent brand. Secondly, marketing executives and advertising agencies can discover whether they can get better value for money in selling a product in this way. Thirdly, academic researchers and economists hoping to understand consumer decisions will benefit from the analysis.

Finally, consumers and consumer groups can become better informed as to whether a celebrity truly values their product or whether it is exploitation in the name of fame. After all, do you know whether Kylie wears her own-brand lingerie, or Celine scents up with her perfume? Does Paul Newman really drizzle his Own salad dressing on his salads? Find out and you will be on to a marketing winner.

"Celebrity entrepreneurship: communication effectiveness through perceived involvement", Int. J. Entrepreneurship and Small Business, 207, Vol. 4, No. 5, pp 505-527