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

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Tue 14 Sep 2004 - 06:04:20 EST


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

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Received on Tue Sep 14 06:08:03 2004

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