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Here are the reasons given by Goodman (2008):

>"Misconception #6: P = .05 means that we have observed data that would occur only 5% of the time under the null hypothesis. That this is not the case is seen immediately from the P value’s definition, the probability of the observed data, plus more extreme data, under the null hypothesis. The result with the P value of exactly .05 (or any other value) is the most probable of all the other possible results included in the “tail area” that defines the P value. The probability of any individual result is actually quite small, and Fisher said he threw in the rest of the tail area “as an approximation.” As we will see later in this chapter, the inclusion of these rarer outcomes poses serious logical and quantitative problems for the P value, and using comparative rather than single probabilities to measure evidence eliminates the need to include outcomes other than what was observed.

[...]

Misconception #7: P = .05 and P <= .05 mean the same thing. This misconception shows how diabolically difficult it is to either explain or understand P values. There is a big difference between these results in terms of weight of evidence, but because the same number (5%) is associated with each, that difference is literally impossible to communicate. It can be calculated and seen clearly only using a Bayesian evidence metric.16"



Thanks for liberating those quotes from the shackles of Elsevier (and fixing the parent).

About the letter 'p': I'd ban the word 'significant' instead if we're going to go there. You could say something like 'null-improbable' if you insisted on using NHST -- such a term would make it harder to forget that it's a fiddly technical concept.




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