[R] yaxis in plot(density(...))
Martin Maechler
maechler at stat.math.ethz.ch
Wed Jul 5 09:38:32 CEST 2006
>>>>> "Taka" == Taka Matzmoto <sell_mirage_ne at 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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