# [R] Help with normal distributions

Dimitris Rizopoulos dimitris.rizopoulos at med.kuleuven.ac.be
Mon Oct 4 12:38:15 CEST 2004

```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

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?
>
>
> Mick
>
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