[R] t.test()

[Peter Dalgaard]

"ONKELINX, Thierry" <Thierry.ONKELINX at inbo.be> writes:

> There is no such thing as an unpaired t-test. A t-test can be a paired,
> one sample or two sample t-test. Since you want to compare the sample
> against a given mean, you need a one sample t-test. You tried to do a
> two sample test. That didn't work because you need at least two
> observations in each group.

NO! This is just plain wrong. 

 
> x <- c(23,25,29,27,30,30)
> t.test(x[-1], mu = x[1])
> 
>         One Sample t-test
> 
> data:  x[-1] 
> t = 5.3634, df = 4, p-value = 0.005833
> alternative hypothesis: true mean is not equal to 23 
> 95 percent confidence interval:
>  25.50814 30.89186 
> sample estimates:
> mean of x 
>      28.2
> 
> 
> Cheers,
> 
> Thierry
> 
> ------------------------------------------------------------------------
> ----
> 
> ir. Thierry Onkelinx
> 
> Instituut voor natuur- en bosonderzoek / Reseach Institute for Nature
> and Forest
> 
> Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
> methodology and quality assurance
> 
> Gaverstraat 4
> 
> 9500 Geraardsbergen
> 
> Belgium
> 
> tel. + 32 54/436 185
> 
> Thierry.Onkelinx at inbo.be
> 
> www.inbo.be 
> 
>  
> 
> Do not put your faith in what statistics say until you have carefully
> considered what they do not say.  ~William W. Watt
> 
> A statistical analysis, properly conducted, is a delicate dissection of
> uncertainties, a surgery of suppositions. ~M.J.Moroney
> 
> -----Oorspronkelijk bericht-----
> Van: r-help-bounces at stat.math.ethz.ch
> [mailto:r-help-bounces at stat.math.ethz.ch] Namens Robin Hankin
> Verzonden: donderdag 23 november 2006 14:12
> Aan: R-help at r-project.org
> Onderwerp: [R] t.test()
> 
> Hi
> 
> I have a vector x of length n.   I am interested in x[1]
> being different from the other observations (ie x[-1]).
> 
> My null hypothesis  is that x[1]
> is drawn from a Gaussian distribution of the same
> mean as observations x[-1], which are assumed
> to be iid Gaussian.   The (unknown) variance
> of x[1] is assumed to be the same as the
> variance of x[-1].
> 
> 
> This should be an unpaired t-test.
> 
> But
> 
> 
>  > x <- c(23,25,29,27,30,30)
>  > t.test(x=x[1] , y=x[-1])
> Error in t.test.default(x = x[1], y = x[-1]) :
>          not enough 'x' observations
>  >
> 
> 
> 
> What arguments do I need to send to t.test() to test my null?
> 
> 
> 
> 
> 
> 
> 
> --
> Robin Hankin
> Uncertainty Analyst
> National Oceanography Centre, Southampton
> European Way, Southampton SO14 3ZH, UK
>   tel  023-8059-7743
> 
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> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 

-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907