Scientists frequently want to answer the question ‘has this treatmenthad an effect?’ Most are unaware that the tests they usuallyuse do not directly address this question. These tests usually posea different question, based on the possibility that nothing hashappened. The question becomes: ‘how probable are these data,if there were NO difference between the original populationsfrom which the data have been randomly drawn?’ (In fact formost laboratory experiments, this supposition is patently false –the experiment has been conducted using a pre-ordained sample,possibly randomly divided into treatment and control groups, butcertainly not randomly sampled.)
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