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In frequentist hypothesis testing, the $p$-value is the probability of a result as extreme (or more) than the observed result, under the assumption that the null hypothesis is true.

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$p$-value Definition

No, you would still use the supremum, so in that case the p-value would be: $$p(x)=\sup_{\theta \in \Theta_0} P_{\theta}(W(X) \leqslant W(x))$$
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3 votes

Kolmogorov Smirnov Test Calculating the P Value Manually

You can find a closed-form matrix method to evaluate the Kolmogorov distribution in Marsaglia et al (2003) and an improved algorithm in Carvalho (2015). This method writes the CDF of the Kolmogorov d …
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2 votes
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Is there a "p-value" for the setting where the assumption is on the alternative?

Yes, it is meaningful Under the stated hypotheses, your p-value function is: $$p_0(x) = \mathbb{P}(X \geqslant x | f_0).$$ If you were to reverse the hypotheses, then your p-value function would be: $ …
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3 votes

Misunderstanding a P-value?

The correct interpretation of a p-value is the conditional probability of an outcome at least as conductive to the alternative hypothesis as the observed value (at least as "extreme"), assuming the nu …
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1 vote
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Do we have to know the distribution in order to calculate p-value?

To get the p-value, we have to either know or estimate/approximate the null distribution of the test statistic. Different types of hypothesis tests use different test statistics and have different nu …
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3 votes

Are p-values computed from the a priori or a posteriori sampling distribution?

The p-value is computed with the sampling distribution Given a parameter $\theta \in \Theta$, an observed data vector $\mathbf{x}$ and a test statistic $T$ that is increasing with respect to evidence …
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9 votes

If p-value is exactly 1 (1.0000000), what should the confidence interval limits be to suppor...

The CI can have any limits, but it is centered exactly around zero For a two-sample T-test (testing for a difference in the means of two populations), a p-value of exactly one corresponds to the case …
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2 votes

Am I using the fisher.test() function incorrectly? Can't replicate p-value found in research...

I do not see any error in your calculations and I am getting the same results as you when I run the various tests at issue (see below for closest result to their reported result). I think the most li …
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2 votes

How do I calculate the posterior probability of a hypothesis given the result of the test?

There is a simple formula for the posterior probability of incorrect/correct inference when rejecting the null One can obtain a simple and elegant posterior result by conditioning on the result of the …
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3 votes

Defining extremeness of test statistic and defining $p$-value for a two-sided test

The answer to this question is what defines the particular test But how do we define what is more extreme? This choice is really the essence of what defines the particular hypothesis test under use. …
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What is the "right" way to define "extreme" in a hypothesis test?

To see if the test is "good" you need to analyse the properties of the power function As you point out, it is possible to derive a test statistic ---and thereby derive the "evidentiary ordering" defin …
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3 votes

Is the following textbook definition of $p$-value correct?

That is the correct definition for a test with a simple null hypothesis. For a test with a composite null hypothesis (i.e., more than one possible parameter value in the null space) things are compli …
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Are my stock returns non-normally distributed?

There is no contradiction between the observation in the QQ plot and the result of the test. Your stock returns have excess kurtosis compared with the normal distribution and this is why the test is …
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Why does this formula produce $p_{2}$ probabilities for Mahalanobis distances?

These values are order statistics, so they follow standard distributional results for those types of statistics. In the case where you have random vectors $\mathbf{X}_1, ..., \mathbf{X}_n \sim \text{ …
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8 votes

Should I trust the $p$-value in statistical tests?

There are an awful lot of issues raised in your question, so I will try to give answers on each of the issues you raise. To frame some of these issues clearly, it is important to note at the outset t …
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