4.9 years ago by

Salt Lake City, UT

Given a test of some effect where p = 0.05 according to some
test-statistic *t*, you expect to see a test-statistic
greater than *t* (or equivalently, a p-value < 0.05) on a test
of random data 5% of the time.

By accepting p = 0.05 for a single test, you're
accepting that there's a 5% chance that effect or difference
may be due to random variation--and that there may not be
an actual "effect" at all.

A consequence of this is that, if the magic number for publication
is p <= 0.05, then, the expected number of publications which have
erroneously rejected their null hypothesis is:

```
p_average * N_publications
```

so, given a fixed p-value cutoff, we can expect the number of falsely
rejected null hypothesis to increase as more papers are published.

Off topic, general statistics question. See http://en.wikipedia.org/wiki/P-value or post to http://stats.stackexchange.com/. Should this one be closed?

17k@all. I think this is a valid question on a bioinformations site, and I think a simple answer like "it's a statistical concept - do some background reading about hypothesis testing" would be valid answer. I had this exact question within a day or two of starting in bioinformatics. I don't see why it should be closed, or even downvoted. The author is not asking for a huge explanation - to quote "can you give me a keyword or something to help me understand what p is about".

3.3k@dole "What is a p-value anyway?: 34 Stories to Help You Actually Understand Statistics" http://www.amazon.com/p-value-Stories-Actually-Understand-Statistics/dp/0321629302

17kCould you quote the sentence in which it was used, or describe the model they were testing please. The keywords I'd go for are 'hypothesis testing', 'null hypothesis', 'probability'.

1.2k@Casey Bergman: TY, that's the answer I was looking for.

200@Casey Bergman: TY. That's the answer I was looking for. The wikipedia link is very valuable.

200Since it was answered in the comments, I think we can close as "no longer relevant".

46kHow is babby formed?

3.0k@all. I think this is a valid question on a bioinformations site, and I think a simple answer like "it's a statistical concept - do some background reading about hypothesis testing" would be valid answer. I have this exact question within a day or two of starting in bioinformatics. I don't see why it should be closed, or even downvoted. The author is asking for a huge explanation - to quote "can you give me a keyword or something to help me understand what p is about".

3.3k@all. I think this is a valid question on a bioinformations site, and I think a simple answer like "it's a statistical concept - do some background reading about hypothesis testing" would be valid answer. I had this exact question within a day or two of starting in bioinformatics. I don't see why it should be closed, or even downvoted. The author is asking for a huge explanation - to quote "can you give me a keyword or something to help me understand what p is about".

3.3k@all. I think this is a valid question on a bioinformations site, and I think a simple answer like "it's a statistical concept - do some background reading about hypothesis testing" would be valid answer. I have this exact question within a day or two of starting in bioinformatics. I don't see why it should be closed, or even downvoted. The author is not asking for a huge explanation - to quote "can you give me a keyword or something to help me understand what p is about".

3.3kI only closed it because the questioner stated "That's the answer I was looking for" in a comment thread, before any real answers were posted. If people think it's useful to leave open, no problem.

46kAbsolutely, completely off topic, and answered as well as it's going to be be answered. So back to closed ;)

13k