Message-ID: <Pine.LNX.4.21.0103271247360.4577-100000@artemis.imbe.med.uni-erlangen.de>
Date: 2001-03-27T10:52:23Z
From: Torsten Hothorn
Subject: How do I generate a random sample with an given variance?
In-Reply-To: <bpn+iHALwFw6EwAb@myatt.demon.co.uk>
> pooh rondstr <poohtest at yahoo.com> writes:
> >Hi R gurus,
> >
> >
> >How do I generate a random sample with a given
> >variance?
>
> Form the standard normal ... for 100 numbers with a mean of 5 and a
> standard deviation of 2:
>
> rnorm(100, mean = 5, sd = 2)
hm, but
R> x <- rnorm(100, mean = 5, sd = 2)
R> mean(x)
[1] 4.742486
R> var(x)
[1] 3.398248
is clearly not what one wants. Better:
R> x <- rnorm(100, mean = 5, sd = 2)
R> x <- (x - mean(x))/sqrt(var(x))
R> mean(x)
[1] 1.385177e-16
R> var(x)
[1] 1
and now create your sample with mean 5 and sd 2:
R> x <- x*2 + 5
R> mean(x)
[1] 5
R> var(x)
[1] 4
Torsten
>
> Mark
>
>
> --
> Mark Myatt
>
>
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