How do you get the truth out of someone who may think it's not in their best interests to tell you it? One answer is to get them to throw a die.
Conservationists working in South Africa to protect wild leopards come up against this problem when interviewing ranchers. They need to find out how many leopards are being killed by ranchers, in order to target their conservation efforts. But they know that the ranchers may be unwilling to tell them the truth, because of the possibility of a fine or prison sentence.
To get round this problem, environmentalists from Bangor University have pioneered the use of a method known as "randomised response technique", sometimes used by public health professionals who interview people engaged in illegal activities, like prostitutes or drug-users.
It works like this. You give the person being interviewed a die, and tell them that before they answer the question they have to throw it, without revealing the number that is rolled. If they roll a one, then they must respond to the question with a "no"; if they throw a six, then they must answer with "yes". All other numbers they have to answer truthfully.
This catch means that when the respondent answers, his or her "yes" may not actually be a truthful "yes"; their "no" might not mean "no". Because of the leeway this gives them, respondents are more likely to open up and give truthful answers on numbers two through five. The forced "yes" and "no" answers introduce a predictable amount of "noise" into the results, but overall the technique gets better answers than a more straightforward approach.
You can read more about this here.
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