R devel - Sep 2004 - propogation of rounding error for t.tests with unequal sample sizes (PR#7225)

# 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

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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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
> 
> 
> 
> This e-mail, including any attachments, is a confidential business
communication, and may contain information that is confidential, proprietary
and/or privileged.  This e-mail is intended only for the individual(s) to whom
it is addressed, and may not be saved, copied, printed, disclosed or used by
anyone else.  If you are not the(an) intended recipient, please immediately
delete this e-mail from your computer system and notify the sender.  Thank you.
> 
> ______________________________________________
> R-devel@stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
> 
> 
-- 
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)
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