Shankar Vedantam has another good column on cognitive bias at the Washington Post. Why are disproven myths still believed? The first impression is the most important for our memory.

Denials of myths actually reinforce myths just by repeating them. People forget the negative tags and it just reinforces the first impression. Don’t forget that confirmation bias also reinforces the mythical belief. As Vedantam said, “Myth-busters, in other words, have the odds against them.”

In one, the CDC handed out fliers to correct myths about the flu vaccine. Within 30 minutes, older people thought 28% of the myths were true. Three days later, they thought 40% of the myths were true. Younger people did better within 30 minutes of reading the flier, but were just as bad three days later.

And, get this, they now believed the CDC was the source of the myth so it became more credible. They forgot the negative tag and confused the sources behind the myth.

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.

Indeed, repetition seems to be a key culprit. Things that are repeated often become more accessible in memory, and one of the brain’s subconscious rules of thumb is that easily recalled things are true.

In politics and elsewhere, this means that whoever makes the first assertion about something has a large advantage over everyone who denies it later.

So if a fraud repeats a myth over and over – it gets imprinted in our minds. Over time, we believe that the myths came from multiple sources and forget whether or not the source was credible. And to top it all off, over time, we forget negative tags. So denials are seen as additional proof that the myth is true.

So, in other words, I’m skeptical of the skepticist movement.

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