Re: [R] significant test

From: Romain Francois <francoisromain_at_free.fr>
Date: Mon 31 Oct 2005 - 23:56:29 EST

Le 31.10.2005 13:45, Prof Brian Ripley a écrit :

> On Mon, 31 Oct 2005, Romain Francois wrote:
>
>> Le 31.10.2005 11:22, Robert a écrit :
>>
>>> I have two groups of data and want to test how the
>>> mean of one group is significant different from the
>>> mean of the other group of data.
>>> which R function can be used?
>>> Thanks.
>>
>> t.test if you assume normality
>> wilcox.test otherwise
>
> Sorry, no.

*I* should be sorry.
Thanks for the correction.

> The Wilcoxon test does NOT test a difference in means: its null
> hypothesis is that the two samples came from the same continuous
> distribution, a much narrower assumption. (It is sensitive to
> differences in variances, for example, and is probably closer to
> testing a difference in medians than means where the shapes of the two
> samples differ)
>
> The Welch two-sample t-test does test exactly the null hypothesis
> stated under normality, and it is pretty insensitive to quite large
> departures from normality. It is unlikely (but possible) that means
> are of primary interest in very-non-normal distributions.

-- 
visit the R Graph Gallery : http://addictedtor.free.fr/graphiques
+---------------------------------------------------------------+
| Romain FRANCOIS - http://francoisromain.free.fr               |
| Doctorant INRIA Futurs / EDF                                  |
+---------------------------------------------------------------+

______________________________________________
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 Tue Nov 01 00:11:22 2005

This archive was generated by hypermail 2.1.8 : Tue 01 Nov 2005 - 03:19:11 EST