Berlin, July 14 (Reuters): Blondes perform intelligence tests more slowly after reading jokes playing on their supposed stupidity, said psychologists in a newly published German study.

Some 80 women of various hair colours were tested on their mental capacity to work quickly and precisely in a series of psychometric tests. Before sitting the tests, half the participants had to read “dumb blonde” jokes, such as: “Why do blondes open yoghurt pots while still at the supermarket? — Because it says: ‘Open Here’ on the lid.”

“No blonde woman believes she is stupid,” said Jens Foerster a social psychologist from the International University Bremen in northern Germany today. “But after exposure to negative social-stereotypes about them, the fair-haired participants performed significantly more slowly in the tests.” Foerster explained the result by saying that when people are told they can't perform a task well, they work more slowly but more cautiously.