# [R] Help with normal distributions

Kjetil Brinchmann Halvorsen kjetil at acelerate.com
Mon Oct 4 16:19:47 CEST 2004

```Dimitris Rizopoulos wrote:

> 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)))
>
Adding to this, what I do, a little bit simpler (?) is:

hist(x, prob=TRUE)
plot( function(y) dnorm(y, mean(x), sd(x)), from=min(x), to=max(x),

Kjetil

> 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?
>>
>>
>> Mick
>>
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>>
>
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>

--

Kjetil Halvorsen.

Peace is the most effective weapon of mass construction.
--  Mahdi Elmandjra

```