Message-ID: <4366147D.5030305@free.fr>
Date: 2005-10-31T12:56:29Z
From: Romain Francois
Subject: significant test
In-Reply-To: <Pine.LNX.4.61.0510311108070.14052@gannet.stats>
Le 31.10.2005 13:45, Prof Brian Ripley a ??crit :
> On Mon, 31 Oct 2005, Romain Francois wrote:
>
>> Le 31.10.2005 11:22, Robert a ??crit :
>>
>>> 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.
--
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| Romain FRANCOIS - http://francoisromain.free.fr |
| Doctorant INRIA Futurs / EDF |
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