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How many police officers are in France?

9th Apr 2014

Last week, we ran a small randomised trial at one of our presentations, which we delivered to a small group of civil servants. Included in the presentation were a series of games to demonstrate some well documented behavioural science effects.

The first of these games was a straightforward demonstration of “anchoring”. The 20 participants were asked to guess the number of police officers in France. The closest guess won a prize of £10 in cash (ponied up by a senior member of staff). Half of the participants randomly received the following piece of information:

“The USA has 794,300 police officers. How many are there in France?”

The other half received this:

“Finland has 7,800 police officers. How many are there in France?”

The correct answer is 220,000.

The average guesses for the two groups were as follows:

Anchoring effects for police officer guess

(n= 29, p<0.05)

We were confident that this would work (anchoring is a very highly replicated effect) but even we were surprised by its effect in this context. Here’s some wisdom from Daniel Kahneman’s Thinking, Fast and Slow:

“The phenomenon we were studying is so common and so important in the everyday world that you should know its name: it is an anchoring effect. It occurs when people consider a particular value for an unknown quantity before estimating that quantity. What happens is one of the most reliable and robust results of experimental psychology: the estimates stay close to the number that people considered— hence the image of an anchor. If you are asked whether Gandhi was more than 114 years old when he died you will end up with a much higher estimate of his age at death than you would if the anchoring question referred to death at 35. If you consider how much you should pay for a house, you will be influenced by the asking price. The same house will appear more valuable if its listing price is high than if it is low, even if you are determined to resist the influence of this number; and so on— the list of anchoring effects is endless. Any number that you are asked to consider as a possible solution to an estimation problem will induce an anchoring effect.”

Kahneman, Daniel (2011-11-03). Thinking, Fast and Slow (Kindle Locations 2117-2124). Penguin UK. Kindle Edition.