Friday, March 27, 2015

P-Value Ban: Small Step for a Journal, Giant Leap for Science

Last month a scientific journal — Basic and Applied Social Psychology — announced that it won’t publish papers that mention the unmentionable P value. No longer will the journal permit published papers to report the P value’s use in the process of “null hypothesis testing,” which psychologists and scientists in many other fields routinely rely on. Anyone embarking on a research career soon gets infected with this method. When you want to test to see whether a food additive causes cancer, or a medicine cures a disease, you assume that it doesn’t — the null hypothesis — and then do an experiment comparing the drug or medicine with a placebo, or another drug, or whatever. If more people survive with the medicine than with the placebo, maybe the medicine works. Or maybe that result was a fluke — the luck of the draw. P values supposedly tell you whether the difference you saw was luck or reality. Except that they don’t. P value calculations tell you only the probability of seeing a result at least as big as what you saw if there is no real effect. more

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