In my future blog this delightful piece would go to section “everyone must know this”, hence reblog!

Popped into the office for a spot of lunch in between induction events and discovered that Jon Butterworth has posted an item on his *Grauniad* blog about how particle physicists use statistics, and the ‘5σ rule’ that is usually employed as a criterion for the detection of, e.g. a new particle. I couldn’t resist bashing out a quick reply, because I believe that actually the fundamental issue is not whether you choose 3σ or 5σ or 27σ but what these statistics mean or don’t mean.

As was the case with a Nature piece I blogged about some time ago, Jon’s article focuses on the p-value, a *frequentist* concept that corresponds to the probability of obtaining a value at least as large as that obtained for a test statistic under a particular *null hypothesis*. To give an example, the null hypothesis might be that two variates are uncorrelated

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