[R] Help with normal distributions

[Dimitris Rizopoulos]

Hi Mick,

regarding your first question try the following,

#if `x' is your data vector, then
y <- seq(min(x), max(x), length=200)
hist(x, prob=TRUE)
lines(y, dnorm(y, mean(x), sd(x)))

regarding your second question, you'd probably want to fit a mixture 
model -> look at package `mclust'.

help(package="mclust")


I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/16/396887
Fax: +32/16/337015
Web: http://www.med.kuleuven.ac.be/biostat/
     http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "michael watson (IAH-C)" <michael.watson at bbsrc.ac.uk>
To: <r-help at stat.math.ethz.ch>
Sent: Monday, October 04, 2004 12:04 PM
Subject: [R] Help with normal distributions


> Hi
>
> I have two questions, the first perhaps dumber than the second.
>
> Firstly, I have a data set, and when I plot a histogram it looks 
> like a
> normal distribution.  So I want to overlay a bell-shaped normal
> distribution on top of it, to demonstrate how similar it is to the
> normal distribution.  I have read the help on dnorm(), rnorm(), 
> pnorm()
> etc but still can't figure out how to plot a normal distribution. 
> Any
> code would be appreciated....
>
> Secondly, and perhaps more difficult, is a second data set.  This, 
> when
> plotted as a histogram, has two clear peaks, perhaps even three, all 
> of
> which look as though they are normally distributed.  So the theory 
> is
> that my data set is actually made up of two, possibly three, 
> underlying
> sub-sets of data which are normally distributed, but with different
> means and standard deviations.  So 1) how do I test for this? And 2) 
> how
> can I estimate the parameters (mean and SD) for the underlying
> distributions?
>
> Thanks in advance for your help
>
> Mick
>
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