Message-ID: <B998A44C8986644EA8029CFE6396A924D89A7B@exqld2-bne.nexus.csiro.au>
Date: 2007-12-01T06:54:09Z
From: Bill Venables
Subject: Quantiles and QQ plots
-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of alfieim29
Sent: Saturday, 1 December 2007 9:26 AM
To: r-help at r-project.org
Subject: [R] Quantiles and QQ plots
I have 20 variables:
5,9,6,1,5,9,7,4,5,6,3,2,4,8,9,6,1,8,4,8
[WNV] I think you have 20 values, not variables.
How do I calculate the corresponding quantiles from a normal
distribution
with the same mean and variance as the sample?
[WNV] There is some ambiguity about this, but a simple way to do it
would be
x <- c(5,9,6,1,5,9,7,4,5,6,3,2,4,8,9,6,1,8,4,8)
n <- length(x)
p <- (1:n - 0.5)/n
z <- qnorm(p, mean(x), sd(x))[order(order(x))]
Also, how do I draw a QQ plot of the data?
[WNV] having done all this you can now just
plot(z, x)
but a much simpler way is
qqnorm(x)
qqline(x)
and don't bother calculating all that stuff!
Thanks for any help!
--
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