From ripley at stats.ox.ac.uk  Mon Sep 13 22:04:20 2004
From: ripley at stats.ox.ac.uk (Prof Brian Ripley)
Date: Mon Sep 13 22:04:31 2004
Subject: [Rd] (PR#7225) propogation of rounding error for t.tests with
	unequal sample sizes (PR#7225)
In-Reply-To: <20040913185742.A1F341138D@slim.kubism.ku.dk>
Message-ID: <Pine.LNX.4.44.0409132102100.23143-100000@gannet.stats>

What are you seeing here?  I get identical results in the two cases.

On Mon, 13 Sep 2004 tucker@mpi.com wrote:

> 
> # users would benefit from a warning about the behavior in the
> # groups.unbalanced case below.  A propogation of difference is the variance
> # calculation is leading to an apparently significant difference in
> # means, even though the numeric values are all identical.  Obviously upon
> # inspection the difference in means is meaningless, but users might be warned
> # if all of the input data is identical

That's not so easy to achieve, given rounding error, but I am seeing
0 variance in both cases.

> xx <- rep(2.10,80)
> 
> groups.balanced <- as.factor(c(rep("one",40),rep("two",40)))
> groups.unbalanced <- as.factor(c(rep("one",44),rep("two",36)))
> 
> t.test(xx ~ groups.balanced)
> 
> t.test(xx ~ groups.unbalanced)
> 
> 
> 
> <<insert bug report here>>
> 
> 
> 
> --please do not edit the information below--
> 
> Version:
>  platform = sparc-sun-solaris2.8
>  arch = sparc
>  os = solaris2.8
>  system = sparc, solaris2.8
>  status = 
>  major = 1
>  minor = 9.0
>  year = 2004
>  month = 04
>  day = 12
>  language = R
> 
> Search Path:
>  .GlobalEnv, package:methods, package:stats, package:graphics, package:utils, Autoloads, package:base
> 
> 
> 
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-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595


[Rd] (PR#7225) propogation of rounding error for t.tests with unequal sample sizes (PR#7225)
Prof Brian Ripley