Putting an image of Shrek, Dora the Explorer or Scooby Doo on packaged children's snacks has a strong influence on a child's perception of how the product tastes, according to new research from Yale University.

Licensed characters such as Shrek have a strong influence on children's snack food preferences. (Paramount Pictures, DreamWorks Animation/Associated Press) North American retailers spend $1.6 billion US each year trying to convince children to consume their products. Often the most effective strategy is to attach a popular children's character to the product. In large measure, however, the characters promote unhealthy foods, the study says.

Published Monday in the journal Pediatrics, the study tested the perceptions of 40 pre-school and Grade 1 children when sampling a selection of graham crackers, gummy fruit snacks and carrots.

The products were presented in plain packaging, and in packaging that contained the likeness of a licensed cartoon character. The children consistently stated they preferred the product with a character on it over the same product in plain packaging.

Cuts both ways

In previous research, the use of a licensed character was helpful in getting children to eat healthier foods. The study authors point to work done by the makers of the TV show Sesame Street, where the image of the character Elmo was stamped on packages of broccoli.

In a Yale study, children consistently chose snack foods with images such as Dora the Explorer. (Mattel, Nickelodeon/Associated Press) When offered a choice between a chocolate bar or a package of broccoli without the Elmo image 78 percent of children chose the chocolate bar. Once Elmo was added to the packaging half the children chose the vegetable over the chocolate bar.

In the case of Shrek, currently one of the most beloved of children's cartoon characters, the study suggests use of the image in multiple marketing efforts leads to confusing and mixed messages.

While Shrek is a spokesman for the U.S. Department of Health and Human Services campaigns, the image is also used by McDonald's, M&Ms and Cheetos.

"These inconsistencies, in which licensed characters are associated with both healthy and unhealthy foods, may send children mixed messages, and this remains an important area for future study," note the authors of the paper.

The Yale researchers conclude that the use of licensed characters on junk food packaging should be restricted.