Bayesian questioning.

Very interesting use of Bayesian reasoning...

Now, Drazen Prelec, a psychologist at the Massachusetts Institute of Technology in Cambridge, US, has devised a scoring system, or “Bayesian truth serum” to encourage people to divulge their honest opinions.

The method relies on asking questions in pairs and analysing the relationship between the answers in a so-called Bayesian approach – which assumes that the answers are interlinked. The first question queries the individual.

For example: "Will you vote in the next presidential election?" or "Have you had more than 20 sexual partners in the last year?" While the second question goes on to focus on the person's estimate of how many other respondents would answer the same way.

It is this perception of what other people’s answer might be which gives hints as to whether the person is telling the truth – especially when their answer is the unusual or unpopular option.

Obviously it doesn't really work on a single person but here's an example on how it could be used in survey research:

For example, he describes a situation where two paintings are viewed by a group of 10 people who are then asked, privately, to pick their favourite. Seven people say they prefer painting A, while three vote for painting B. If, on the second question, all 10 people said they thought everyone else would prefer painting A, then those three people expressing a personal preference for painting B might be thought of as a safer bet for having told the truth. That is because, argues Prelec, despite what they thought was more popular, those individuals still chose the other painting.