December 31st, 2004


fun with probability

Quote from

Last Thursday, Dec. 23, scientists announced that a space rock named 2004 MN4 had about a 1-in-300 chance of striking Earth on April 13, 2029. On Friday, the risk was upgraded as more observations rolled in. The asteroid was given an unprecedented risk rating of 4 on the Torino Scale, which means it warrants careful monitoring. The odds at various times were put at 1-in-63 and 1-in-45.

As of Monday, the chances of an impact on April 13, 2029 stood at about 1-in-40, or 2.6 percent.

Experts point out that means a 97.4 percent chance the giant boulder will miss, and they stress that the odds are likely to go down to zero, eventually, when more detailed observations of its path are made.


"Likely to go down to zero". Like, say, a 97.4% chance? But unfortunately there's a 2.6% chance that the odds will go to 1 . . .

Saying "1 in 40, but likely to go to zero" is the SAME THING AS SAYING 1 IN 40.

And if you think that, for some reason, there's more than a 1 in 40 chance that the odds will go to 0 . . . then why not factor that into your odds?

(Note: last I heard, the odds were more along the lines of "1 in 500 million", so they did, in fact, effectively go to 0. But my point still stands.)