[R] QQ plot for normality testing

[Greg Snow]

I would use the vis.test function along with vt.qqnorm (both in TeachingDemos package).  This will create several plots, one of which is your data, the rest are simulated normals with the same mean and standard deviation.  If you can tell which plot stands out (and it is your real data) then that suggests that the data is not normal.  If you cannot tell which plot is the real data then that suggests that your data is close enough to normal.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Matevž Pavlic
> Sent: Saturday, April 30, 2011 11:28 AM
> To: r-help at r-project.org
> Subject: [R] QQ plot for normality testing
> 
> Hi all,
> 
> 
> 
> I am trying to test wheater the distribution of my samples is normal
> with QQ plot.
> 
> 
> 
> I have a values of water content in clays in around few hundred
> samples. Is the code :
> 
> 
> 
> qqnorm(w)      #w being water content
> 
> qqline(w)
> 
> 
> 
> 
> 
> sufficient?
> 
> 
> 
> How do I know when I get the plots which distribution is normal and
> which is not?
> 
> 
> 
> Thanks, m
> 
> 
> 	[[alternative HTML version deleted]]
> 
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