Michael Shermer: Why Our Brains Do Not Intuitively Grasp Probabilities

[Orphia Nay]

For your reading pleasure.

Scientific American Magazine - September 3, 2008

Why Our Brains Do Not Intuitively Grasp Probabilities

Part one of a series of articles on the neuroscience of chance

By Michael Shermer

Have you ever gone to the phone to call a friend only to have your friend ring you first? What are the odds of that? Not high, to be sure, but the sum of all probabilities equals one. Given enough opportunities, outlier anomalies—even seeming miracles—will occasionally happen.

Let us define a miracle as an event with million-to-one odds of occurring (intuitively, that seems rare enough to earn the moniker). Let us also assign a number of one bit per second to the data that flow into our senses as we go about our day and assume that we are awake for 12 hours a day. We get 43,200 bits of data a day, or 1.296 million a month. Even assuming that 99.999 percent of these bits are totally meaningless (and so we filter them out or forget them entirely), that still leaves 1.3 “miracles” a month, or 15.5 miracles a year.

Thanks to our confirmation bias, in which we look for and find confirmatory evidence for what we already believe and ignore or discount contradictory evidence, we will remember only those few astonishing coincidences and forget the vast sea of meaningless data.

We can employ a similar back-of-the-envelope calculation to explain death premonition dreams.
[...]

 

[drkitten]

For your reading pleasure.

I'd also recommend Kahnemann and Tversky and their parable of Linda, the (feminist?) bank teller.

 

[Bikewer]

A well-stated summary of ideas I've tried to point out for years. (less well-stated....)

 

[Rodney]

For your reading pleasure.

So all coincidences and premonitions can be dismissed by "assign[ing] a number of one bit per second to the data that flow into our senses as we go about our day"?

 

[Soapy Sam]

7 bits/sec is the more common figure for mental activity. But how many bits are required to compose a miraculous message?
I'd say a meaningful one bit message would indeed be fairly improbable. Even "NO" comprises rather more than one bit.

 

[Dunstan]

I don't have my copy handy, but I believe Richard Dawkins' book A Devil's Chaplain contained an essay along similar lines that I would also recommend.