[R] Help interpreting density().
rkevinburton at charter.net
rkevinburton at charter.net
Tue Jul 29 06:14:46 CEST 2008
I issue the following:
> d <- density(rnorm(1000))
> d
and get:
Call:
density.default(x = rnorm(1000))
Data: rnorm(1000) (1000 obs.); Bandwidth 'bw' = 0.2235
x y
Min. :-3.5157 Min. :2.416e-05
1st Qu.:-1.6892 1st Qu.:1.129e-02
Median : 0.1373 Median :7.267e-02
Mean : 0.1373 Mean :1.367e-01
3rd Qu.: 1.9639 3rd Qu.:2.693e-01
Max. : 3.7904 Max. :4.014e-01
The documentation indicates that the bw is essentially the sd. Yet I have specified an sd of 1? How am I to interpret the ranges of the values? x ranges almost from -4 to +4 and y ranges from 0 to 0.4. The mean x is .1 which isn't too awfully close to what I would expect (0.0). Then there is:
> d <- density(rpois(1000,0))
> d
Call:
density.default(x = rpois(1000, 0))
Data: rpois(1000, 0) (1000 obs.); Bandwidth 'bw' = 0.2261
x y
Min. :-0.6782 Min. :0.01979
1st Qu.:-0.3391 1st Qu.:0.14073
Median : 0.0000 Median :0.57178
Mean : 0.0000 Mean :0.73454
3rd Qu.: 0.3391 3rd Qu.:1.32830
Max. : 0.6782 Max. :1.76436
Here I am getting the mean that I expect from a Poisson distribuition but y ranges from 0 to 1.75. Again I am not sure what these numbers mean. How can I map the output to the standard distirbution description parameters?
Thank you.
Kevin
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