Rory Sutherland Columnist I All else being equal most cases of murder where there is a history of spousal abuse were dont know the answer to this question, but I would like committed by the spouse. your opinion. When asked on a form to state your religion or ethnicity, should you leave the section blank? Or might I dont suppose one person in a hundred would instinctively it be better to lie, or answer other? Or would it be better understand this distinction without having it explained. No-one in to tell the truth? Under perfect conditions, I would, of course, tell the courtroom challenged it. Yet the subtle distinction here aects the truth. The problem is, perfect conditions never exist. the jurors likely inference by a factor of more than 2,200 from And heres my issue. It seems to me an inarguable law that a 0.04% implication of guilt to perhaps 89%. there must be far more semi-competent or indierent statisticians Wider context also matters in the assessment of DNA evidence. among the population than there are great statisticians. If we If one in 200,000 people, including the suspect, shares DNA with assume a normal distribution of statistical competence, there will the perpetrator, you have to consider how that DNA was first be a left-hand tail of people who are shockingly bad at assessing used. If it was used to find a suspect (perhaps by trawling a and understanding statistics, a large rump in the middle of people database of two million people) it has little value. If, on the other who are quite poor, then an equally large group of people who hand, someone seen fleeing the scene is arrested and found to are confident enough to be dangerous. Tailing o towards the have such a match, it adds to a reasonable presumption of guilt. right will be a tiny number of true experts. Contextual blindness of this kind led to the unsafe convictions of Im not worried by the people who are atrocious at statistics. Sally Clark in the UK and Lucia de Berk in the Netherlands. When they are wrong, it is easy for many people to spot and Heres why I am slightly alarmed by correct their errors. What worries me is surveys routinely containing questions the profusion of GCSE-level statisticians, It seems a peculiar property about ethnicity or religion, but that fail because it seems to me a peculiar of statistical understanding that to collect enough information to provide property of statistical understanding that high, but not spectacular, ability wider context. For every valuable finding high, but not spectacular, ability may be may be worse than none that emerges, we may end up with 10 worse than none. In statistical questions, spurious findings spurious it is possible to be confidently and correlations, or those that are blind to monumentally wrong, yet for the the many confounding variables that simply arent collected. fallaciousness of your inference to be invisible to large groups of There is, for instance, a significant correlation between your otherwise educated people especially yourself. Here, a little own personal success and the number of books your parents learning really is a dangerous thing. Take the OJ Simpson trial: owned. I have never been asked for that information on a form. This is not to deny racial inequality or bias. It is simply a question When the prosecution presented evidence that Simpson had of understanding it better. To lump together someone who arrives been violent toward his wife, the defence argued that there was in Britain as a newly qualified surgeon and someone who arrives only one woman murdered for every 2,500 women who were in later life with no qualifications simply because they share skin subjected to spousal abuse, hence any history of Simpson being colour is not illuminating it is misleading. Our selective violent toward his wife was irrelevant to the trial. collection of data risks doing exactly that. The act of averaging also risks blinding us to areas where racial bias is most acute. Yet, according to Gerd Gigerenzer, the correct probability Data broken down by race and nothing else will lead us to requires the wider context that Simpsons wife had not only been believe that all inequality proceeds from overt or unconscious subjected to domestic violence, but rather subjected to domestic bias, while leaving unseen the influence of other things (social violence (by Simpson) and killed (by someone). Gigerenzer writes networks in particular) that may play an even more powerful role the chances that a batterer actually murdered his partner, given in perpetuating inequality. The practice is largely well intentioned. that she has been killed, is about eight in nine, or approximately Whether it is helpful is a dierent question. 90%. While most cases of spousal abuse do not end in murder, 7 Impact ISSUE 38 2022_pp6-7_Rory.indd 7 22/06/2022 14:40