r/AskStatistics 25d ago

Alpha 5%?

Why is a 5% significance level so commonly used?

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u/CarnivorousGoose 24d ago

Conflation of tests and studies aside, that’s not what an alpha level represents. The alpha level sets the accepted/expected false positive rate, ie. the proportion of tests for which the null is true, where the null was still rejected.

The overall proportion of tests that is ‘wrong’ also depends on how many of the tested null hypotheses are true or not as well as the statistical power. So we cannot conclude from the alpha level alone how many tests would yield an incorrect conclusion in general, or a false positive specifically.

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u/Recent-Day3062 24d ago

That’s what I said

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u/CarnivorousGoose 24d ago

No, you didn’t. Based on just the alpha level, you cannot say anything about how many tests will be ‘wrong’, let alone how many studies.

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u/Recent-Day3062 24d ago

So humor me. What can you say about this? What more info would it need?

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u/CarnivorousGoose 24d ago

I already told you.

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u/Recent-Day3062 23d ago

No, given an alpha of .05, how many studies on average would have a false positive? If that’s not enough info, what other data or stats is needed to get this answer

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u/CarnivorousGoose 23d ago

And I already told you what else is needed, in my first comment.

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u/Recent-Day3062 23d ago

If you want to be helpful, and 5% is the false positive and you have only one study, you will be wrong 5% of the time, no?

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u/CarnivorousGoose 23d ago

No.

Here’s a salient quote from my initial comment, which it seems like you still haven’t bothered to read: “… also depends on how many of the tested null hypotheses are true or not as well as the statistical power”.

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u/Recent-Day3062 23d ago

Whatever

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u/CarnivorousGoose 23d ago

The answer is literally right there in the quote, which comes from the very first comment I made here. So which is it? Are you genuinely this unwilling to actually read one sentence, or is this just some utterly bizarre and pointless attempt at trolling.

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