# Meaning of "or 1 in p" in Wikipedia article on Normal Distribution

I was taking a closer look at this table in the Wikipedia article https://en.wikipedia.org/wiki/Normal_distribution#Standard_deviation_and_coverage.

It is the 4th column labeled or 1 in p that I'm having trouble with. It seems to be the inverse of the 3rd column, 1-p. What is the meaning of or 1 in p?

• This is the value of $1/(1-p)$, there is one chance out of $3.1514$, $21.978$, &tc. to fall outside the interval. Nov 21 at 6:04

It is indeed the inverse of $$1-p$$. The column is mislabelled, since $$p$$ is already defined.
They are writing $$1-p$$ as a fraction $$1/M$$, and telling you $$M$$. It can get hard to compare very small fractions intuitively, but writing them as $$1$$ in $$M$$ can be more intuitive (e.g. "how many times would we need to repeat this sampling from a normal, to expect to see one value at least this many SDs from the mean?". Framed this way, it's effectively a "return period", which is a common way to express rare events like floods or extreme storms.)