We have had some chilly months here in Minnesota, but ….
Earth had third warmest May on record (tie with 1998 and 2005)
The global temperature has been above average now 339 straight months (more than 28 years). The last time global temperatures were below average (February, 1985), the Chevrolet Celebrity was among the top selling cars.
Leaked NSA slide-deck claims that NSA has “direct access” to servers at Google, Apple, Facebook, Skype, Yahoo, and many others
This story has received a lot of coverage in the last few days, even extending to Jay Leno’s monologue. Understandably, there is a lot of concern about the civil liberties implications. But there is also another question, answered by Corey Chivers: How likely is the NSA PRISM program to catch a terrorist?
We don’t really know anything about how PRISM works (NSA = Never Say Anything), but with some plausible assumptions we can estimate the answer. Suppose
- If a terrorist is in the system, the probability is 99% that PRISM will flag him/her.
- An good guy has only a 1/100 chance of being flagged as potential terrorist.
- The actual number of terrorists is quite small, say 1 in 1,000,000.
Using Bayes’ rule, Chivers shows that only 1 in 10,102 of the people flagged as suspects will actually be a terrorist!
From Bayes: How one equation changed the way I think
Bayes’ Rule is a simple formula that tells you how to weigh evidence and change your beliefs. I don’t go around plugging numbers into a formula all the time, but nevertheless, becoming familiar with Bayes has shifted the way I think in some important ways.
Irish Class, JUne 3, 2013
Rang Gaeilge, 3ú lá Mí na Mheiteam 2013