From: Robert Mcfadden <robert-mcfadden_at_o2.pl>

Date: Thu 13 Jul 2006 - 17:03:03 EST

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu Jul 13 17:06:47 2006

Date: Thu 13 Jul 2006 - 17:03:03 EST

> -----Original Message-----

*> From: r-help-bounces@stat.math.ethz.ch [mailto:r-help-
**> bounces@stat.math.ethz.ch] On Behalf Of Matthew.Findley@ch2m.com
**> Sent: Wednesday, July 12, 2006 11:14 PM
**> To: r-help@stat.math.ethz.ch
**> Subject: [R] shapiro.test() output
**>
**> R Users:
**>
**> My question is probably more about elementary statistics than the
**> mechanics of using R, but I've been dabbling in R (version 2.2.0) and
**> used it recently to test some data .
**>
**> I have a relatively small set of observations (n = 12) of arsenic
**> concentrations in background groundwater and wanted to test my
**> assumption of normality. I used the Shapiro-Wilk test (by calling
**> shapiro.test() in R) and I'm not sure how to interpret the output.
**> Here's the input/output from the R console:
**>
**> >As = c(13, 17, 23, 9.5, 20, 15, 11, 17, 21, 14, 22, 13)
**> >shapiro.test(As)
**>
**> Shapiro-Wilk normality test
**>
**> data: As
**> W = 0.9513, p-value = 0.6555
**>
**> How do I interpret this? I understand, from poking around the internet,
**> that the higher the W statistic the "more normal" the data.
**>
**> What is the null hypothesis - that the data is normally distributed?
**>
**> What does the p-value tell me? 65.55% chance of what - getting
**> W-statistic greater than or equal to 0.9513 (I picked this up from the
**> Dalgaard book, Introductory Statistics with R, but its not really
**> sinking in with respect to how it applies to a Shipiro Wilk test).?
**>
**> The method description - retrieved using ?shapiro.test() - is a bit
**> light on details.
**>
**> Thanks much.
*

The null hypothesis: the data is normally distributed. If p-value > \alpha (significance level) it means that there is no evidence to reject null hypothesis. Otherwise you reject - your data is not normally distributed.

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu Jul 13 17:06:47 2006

Archive maintained by Robert King, hosted by
the discipline of
statistics at the
University of Newcastle,
Australia.

Archive generated by hypermail 2.1.8, at Thu 13 Jul 2006 - 18:14:27 EST.

*
Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help.
Please read the posting
guide before posting to the list.
*