Dice Help Scientists Get Honest Answers to Touchy Questions

By Veronique Greenwood | August 2, 2011 3:58 pm

New tools for conservation?

What’s the News: Maybe it’s you—or maybe it’s the dice. A technique that relies on concealing individual transgressions while revealing greater truths is letting biologists get to the bottom of South African farmers’ killing of leopards.

What’s the Context:

  • In South Africa, there’s constant tension between carnivores and local farmers, who may kill animals they perceive as a threat to livestock.
  • Knowing whether farmers are doing this helps conservationists understand the driving forces behind animals’ extinction and plot countermeasures, but since killing carnivores like leopards and brown hyenas is illegal, it’s hard to get a straight answer from farmers about their activities.
  • Enter the randomized response technique, which was first developed in 1965. Also used by social scientists to get people to talk about their sex lives, it lets researchers see overall trends in taboo behavior without being able to pin a crime or an embarrassing behavior on any one person.

How the Heck:

  • First, a researcher gave a farmer a die, which the farmer could roll without the researcher seeing its outcome.
  • Then, the researcher asked questions like “In the last 12 months, did you kill any leopards?,” and before the farmer answered, he rolled the die. If he rolled a 1, he should say “no,” no matter what the correct answer was, and say “yes” if he rolled a 6. For all the other numbers, he should answer honestly. The fact the researcher never had any way of knowing whether the farmer was saying “yes” because it was the truth or because he rolled a 6 gave the subject a sense of safety.
  • But after recording all the answers provided by their subjects, the researchers found that farmers said they had killed leopards far more frequently than one in six times, which is what would have been expected had they only admitted to the crime when the die made them. Under the cover of the die, farmers were admitting to having killed the creatures.
  • In fact, judging from the results, at least 19% of the 99 subjects had killed leopards in the last year. That’s quite a bit more than researchers were expecting.

The Future Holds: These results will influence conservationists’ approaches in the future. For instance, now that they can see how strongly farmers believe leopards are a threat to livestock, they can work to instate programs that replace lost cattle after leopard attacks, perhaps reducing local hostility. But it’s not clear that the technique will remain useful for other, similar projects once people know how it works, or whether people in rural areas who hold particular grudges against government interference will play by the rules of the game. They might, after all, just reply randomly.

Reference: St. John et al. Identifying indicators of illegal behaviour: carnivore killing in human-managed landscapes. Published online before print July 27, 2011, doi: 10.1098/rspb.2011.1228 Proc. R. Soc. B

[via New Scientist]

Image courtesy of topher76 / flickr

CATEGORIZED UNDER: Environment, Mind & Brain, Top Posts
  • Dee Sallows

    Lateral thinking in science is rare. I enjoy seeing it in your magazine.

  • http://www.nicky510.com Crow

    That’s always an issue – whether the player is actually playing by the rules. It’s a really tough one to assess. But, as Dee said, it’s nice to think a little bit out of the box and not simply ask questions that one knows won’t get accurate answers.

  • kirk

    Now we will include a pair of dice with the 1040 form — Tax Reform!

  • Hollander

    Even under the safety of the die, I find it weird that people will speak the truth about killing leopards. After all, I imagine every person with common sense might realise that the probability of him having to give an honest answer is 4/6, where only 1/6 probability would mask his true answer as “forced by the die”. Personally, I don’t like those odds, but I guess this is quite an interesting mind trick on people.

  • phanmo

    I feel there is a kind of “plausible deniability”; it’s not difficult to calculate the odds as being in favour of giving an honest answer, but no one could ever point at someone and say “He killed a leopard” based on the responses to this survey. It’s not so much about the actual odds as about having a security blanket.

    Also, I think that we all know that most people don’t care about odds, based on the number of people who play the lotto or gamble in casinos.

  • daddyvortex

    Is this a little bit like the old firing squad policy where the commander of the squad tells the men that one of the members has been issued a blank round at random? The men do not get to see their rifles loaded. The goal is to ensure as many men fire at the condemned as possible, yet assuage the feelings of the soldiers in their role as executioner.

  • Naveed

    Pretty clever idea….

    Anyone else think it’s unfair that we force people in poor and developing countries to live with predatory animals even though we killed all of ours? I mean I understand the animals are cool and play a key role in the natural food chain but humans have done fine taking their position at the top of the food chain in Europe and North America.

  • kyle

    I’m surprised the researchers were surprised at the results. 19% of the participants said they had killed a leopard (or multiple), and the probability of getting a 6 would be about 16.5%. that’s only a 2.5 difference. out of 99 that would mean it was POSSIBLE that 16 people rolled a six, thereby forced to answer with a “yes”, leaving only 3 others that rolled differently and answered honestly. of course there could have been those that have killed, but forced to answer “no” with the same probability. not surprising results at all when AT LEAST 16.5% of the participants are always going to “confess” to killing a leopard.

  • bill

    This same method can be used to track presence of hostile motives in internet search traffic and possibly serve as a tool for identifying threat factors contingent to terrorist activities/or other.

    Surely, the NSA is aware of this obvious application??? Semiotics, Mr. Watson… Semiotics.


  • bill

    This MEANS that you can’t NOT tell on yourself…

    Under informed examination, there can be no secrets…

  • MomRose

    The article didn’t say “19% of the participants said they had killed” leopard(s). It said “judging from the results, at least 19% of the 99 subjects had killed leopards in the last year.” I would suppose that researchers know how to determine statistically what likely percentage of leopard killers they are talking to from whatever raw data they do collect.

  • Stan

    Kyle [at 8.] misinterpreted the results. The researchers report their finding that 19% of 99 people questioned were determined to have killed a leopard. That is NOT the same as Kyle’s interpretation that 19% said that they had killed a leopard. The research would have already deducted the estimated random “Yes” answers from the total. Expected random “Yes”, if none of 100 [simplify the percentages] questioned did, in fact, kill a leopard would be 17 “Yes”, with the rest “No”. And included in the 83 “No” would be 17 mandatory “No” and 66 truthful “No”.

    In the case of 19 of 100 actually killing a leopard, and assuming these 19 are proportionally rolling 1/6th One, 2/3rds Two to Five, and 1/6th Six, the expected breakdown in the ANSWERS would be 29-1/2 “Yes”, the rest “No”. From those answers, the researchers can back out the estimate of 19% who did, in fact, kill one or more leopards.


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