Ben Goldacre, The Guardian, Saturday 4 December 2010

Why do clever people believe stupid things? It’s difficult to make sense of the world from the small atoms of experience that we each gather as we wander around it, and a new paper in the British Journal of Psychology this month shows how we can create illusions of causality, much like visual illusions, if we manipulate the cues and clues we present.

They took 108 students and split them into two groups. Both groups were told about a fictional disease called “Lindsay Syndrome”, that could potentially be treated with something called “Batarim”. Then they were told about 100 patients, slowly, one by one, each time hearing whether the patient got Batarim or not, and each time hearing whether they got better.

Now, when you’re hearing about patients one at a time, in a dreary monotone, it’s hard to piece together an overall picture of whether a treatment works (this is one reason why, in evidence based medicine, “expert opinion” is ranked as the least helpful form of information). So while I can tell you that overall, in these results, 80% of the patients got better, regardless of whether they got Batarim or not – the drug didn’t work – this isn’t how it appeared to the participants. They overestimated its benefits, as you might expect, but the extent to which they overestimated its effectiveness depended on how the information was presented.

The first group were told about 80 patients who got the drug, and 20 patients who didn’t. The second group were told about 20 patients who got the drug, and 80 patients who didn’t. That was the only difference between the two groups, but the students in the first group estimated the drug as more effective, while the students who were told about only 20 patients receiving it were closer to the truth.

Why is this? One possibility is that the students in the second group saw more patients getting better without the treatment, as so got a better intuitive feel for the natural history of the condition, while the people who were told about 80 patients getting Batarim were barraged with data about people who took the drug and got better.

This is just the latest in a whole raft of research showing how we can be manipulated into believing that we have control over chance outcomes, simply by presenting information differently, or giving cues which imply that skill had a role to play. One series of studies has even shown that if you manipulate someone to make them feel powerful (by remembering a situation in which they were powerful, for example) then they imagine themselves to have even greater control over outcomes that are still purely determined by chance, which perhaps goes some way to explaining the hubris of the great and the good.

We know about optical illusions, and we’re familiar with the ways that our eyes can be misled. It would be nice if we could also be wary of cognitive illusions that affect our reasoning apparatus, but more than that, like the “close door” buttons in a lift – which, it turns out, are often connected to nothing at all – these illusions are modern curios.