# Re: [R] yaxis in plot(density(...))

From: Martin Maechler <maechler_at_stat.math.ethz.ch>
Date: Wed 05 Jul 2006 - 17:38:32 EST

>>>>> "Taka" == Taka Matzmoto <sell_mirage_ne@hotmail.com>
>>>>> on Wed, 05 Jul 2006 00:19:13 -0500 writes:

Taka> Dear R-users
Taka> Could you explain what is the unit of yaxis in plot(density(...))?

Taka> It says "density" but it is unclear to me what density is.

This is really not a question about R, but about first-level probability and statistics:

The unit of a density {estimated or not}

f(x) is 1 / (unit of x),
since one of the major properties of a density is \int f(x) dx == 1 and the latter is dimension free'' (as others would say).

E.g. the unit in plot(density(faithful\$eruptions)) is

1 / min aka '[min ^{-1}]' (min = minutes of eruption time)

Martin Maechler, ETH Zurich

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