I am seeing NaNs, which is more sensible.
We will add a test for stderr small compared to the larger group mean.
On Mon, 13 Sep 2004, Tucker-Kellogg, Gregory wrote:
>
> My apologies for not including the transcript in the original message:
>
> > 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)
>
> Welch Two Sample t-test
>
> data: xx by groups.balanced
> t = 0, df = 78, p-value = 1
> alternative hypothesis: true difference in means is not equal to 0
> 95 percent confidence interval:
> -4.004247e-16 4.004247e-16
> sample estimates:
> mean in group one mean in group two
> 2.1 2.1
>
> > t.test(xx ~ groups.unbalanced)
>
> Welch Two Sample t-test
>
> data: xx by groups.unbalanced
> t = -4.1007, df = 54.298, p-value = 0.0001388
> alternative hypothesis: true difference in means is not equal to 0
> 95 percent confidence interval:
> -1.322366e-15 -4.539911e-16
> sample estimates:
> mean in group one mean in group two
> 2.1 2.1
>
>
>
> >-----Original Message-----
> >From: Prof Brian Ripley [mailto:[EMAIL PROTECTED]
> >Sent: Monday, September 13, 2004 4:04 PM
> >To: Tucker-Kellogg, Gregory
> >Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED]
> >Subject: Re: [Rd] (PR#7225) propogation of rounding error for
> >t.tests with unequal sample sizes (PR#7225)
> >
> >
> >What are you seeing here? I get identical results in the two cases.
> >
> >On Mon, 13 Sep 2004 [EMAIL PROTECTED] 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.
> >>
> >> ______________________________________________
> >> [EMAIL PROTECTED] mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-devel
> >>
> >>
> >
> >--
> >Brian D. Ripley, [EMAIL PROTECTED]
> >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
> >
> >
>
>
>
> 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.
>
> ______________________________________________
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>
>
--
Brian D. Ripley, [EMAIL PROTECTED]
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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