In light of the "new evidence" claims that are making the rounds, the Per Cale blog has an interesting post on myths and cognitive biases

...It seems that myth denial with accurate information may actually reinforce the myth.

University of Michigan researcher Norman Schwarz had volunteers read a flier from the Centers for Disease Control about flu vaccination myths. Within 30 minutes of reading the flier, older adults recalled 28% of the false statements as being true. After 3 days, they thought 40% of the myths were factual.¹

Younger people did better at first, but three days later they made as many errors as older people did after 30 minutes. Most troubling was that people of all ages now felt that the source of their false beliefs was the respected CDC.¹

...So denying myths actually reinforces them to some extent.The experiments do not show that denials are completely useless; if that were true, everyone would believe the myths. But the mind's bias does affect many people, especially those who want to believe the myth for their own reasons, or those who are only peripherally interested and are less likely to invest the time and effort needed to firmly grasp the facts.

The research also highlights the disturbing reality that once an idea has been implanted in people's minds, it can be difficult to dislodge. Denials inherently require repeating the bad information, which may be one reason they can paradoxically reinforce it.

Shankar Vedantam. Persistence of Myths Could Alter Public Policy Approach.
Washington Post. September 4, 2007. Page A03.
http://www.washingtonpost.com/wp-dyn/content/article/2007/09/03/AR2007090300933_pf.html

And this interesting post by John Allen Paulos on three common cognitive biases