Absence of evidence IS evidence of absence

The other day, I came across a rather illuminating little proof.

Taken from Kim Oyhus’ website.

For those of us who don’t remember Bayesian probability too well, ponder this:
A= You have a Body Mass Index over 25.
B= You’re obese.

Having a BMI over 25 means you’re obese.

An absence of any proof that your BMI is over 25 means that you’re probably not obese, because there are fewer obese people.
QED.

I now wish that people nuts would stop misquoting Carl Sagan by saying “Absence of evidence is not evidence of absence” whenever they talk about UFOs, alien abductions, telekinesis, conspiracy theories, and other miscellaneous bullshit.

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