A nice explanation...

[alexpgp]

Cory Doctorow, writing on innumeracy and the threat to freedom (at the Guardian):

Our innumeracy means that our fight against these super-rarities is likewise ineffective. Statisticians speak of something called the Paradox of the False Positive. Here's how that works: imagine that you've got a disease that strikes one in a million people, and a test for the disease that's 99% accurate. You administer the test to a million people, and it will be positive for around 10,000 of them – because for every hundred people, it will be wrong once (that's what 99% accurate means). Yet, statistically, we know that there's only one infected person in the entire sample. That means that your "99% accurate" test is wrong 9,999 times out of 10,000!

Nicely presented.

And now, I really must hit the sack.

Cheers...

Comments

[baikonur.livejournal.com]

My last semester of law school I wrote a paper about statistical analysis of catastrophic harm. The literature on the subject suggests that the high cost in (in lives) of an extremely low-probability catastrophe can make even low probability events worth considering.

[alexpgp.livejournal.com]

Worth considering, yes.

However, the Paradox of the False Positive suggests that increasing the size of the haystack to find the same needles is not the way to go.

Cheers...