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We know intuitively how many lay opinions outweigh an expert

23 October 2017

Imagine contemplating which treatment to undertake for a health problem. Your specialist explains there are two possibilities, and strongly endorses one as right for you.

But when you discuss it with a friend, she suggests that based on what she’s heard, the other would be better. Another friend, the same. And another. Does there come a point where the friends outweigh the expert?

Given enough information – the accuracy of the expert in the past, the degree to which the public have any insight on the issue – you can in theory mathematically “solve” this issue with a probabilistic model. In fact, according to new research published in Thinking and Reasoning, that’s exactly what we do intuitively and with a high degree of accuracy.

In a collaboration between Radboud University Nijmegen and University College London, Jos Hornikx’s team asked 146 Dutch adults, most commonly educated to graduate level with an average age of 31, to evaluate five scenarios each involving a public policy decision such as whether to create car-free zones in a city and whether it would impact the number of shop customers. In each scenario, an expert (in this case, a professor of retail marketing) had given a recommendation for or against the proposal, and participants were told their track record – e.g. they had been correct in 80 per cent of previous zoning decisions.

Each participant was also told that a subset of the public – for example, local road workers (with no formal training in the topic) – had disagreed with the expert view. Participants were told how much these non-experts had insight into the relevant issues – this varied from participant to participant, with some told the non-experts had been correct only 51 per cent of the time, others as high as 60 per cent. Participants were then asked how many non-experts would need to hold a dissenting view to outweigh the single expert.

Read more on our Research Digest blog.

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