Tim wrote:

Not a new idea. Ted Nelson (IIRC) wrote about using coin flips to randomize AIDS poll questions. ("Have you engaged in unprotected sex?" Flip a coin and XOR it with your actual answer.) I remember talking to Eric Hughes, Phil Salin, and others around 1990-91 about this.

[snip]

The idea is that the pollee XORs his answer with a random bit. His answer then doesn't _implicate_ him, but overall statistics can still be deduced from a large enough sample.

Uh, excuse me?! I can see how such an idea works if you add a random variable with a known mean to the data. A researcher could do this before storing the data, in order to protect the confidentiality of individual respondents, and still be able to compute aggregate statistics. However, if you XOR a bit with a random bit, you have something equally likely to be in either state. Even a large collection of yes/no responses XORed with random bits is indistinguishable from random data. So I am afraid I must give the prior message my coveted "Silliest Thing Said On the Internet This Week" award. <Chortle> -- Eric Michael Cordian 0+ O:.T:.O:. Mathematical Munitions Division "Do What Thou Wilt Shall Be The Whole Of The Law"