23 Nov 2006 14:48:31 +0100, Peter Dalgaard <[EMAIL PROTECTED]>: > "ONKELINX, Thierry" <[EMAIL PROTECTED]> 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.
I agree. Hoping I'm not missing anything, something like: > t.test(x[1],x[-1], var.equal=TRUE) should work, since pooled variance can be computed if length(x)>2. But, surprising, this still gives "not enough 'x' observations". I've seen that's because length of the first argument in t.test is checked before checking 'var.equal' value in 't.test.default'. I'm wrong, or 2 sided test should be computed as: t.test.value <- abs(x[1]-mean(x[-1]))/var(x) t.test.pvalue <- 2*pt(-t.test.value, length(x)-2) ? > > > > 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 > > > > [EMAIL PROTECTED] > > > > 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: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] Namens Robin Hankin > > Verzonden: donderdag 23 november 2006 14:12 > > Aan: [EMAIL PROTECTED] > > 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 > > > > ______________________________________________ > > R-help@stat.math.ethz.ch mailing list > > https://stat.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide > > http://www.R-project.org/posting-guide.html > > and provide commented, minimal, self-contained, reproducible code. > > > > ______________________________________________ > > R-help@stat.math.ethz.ch mailing list > > https://stat.ethz.ch/mailman/listinfo/r-help > > 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 Ă˜ster Farimagsgade 5, Entr.B > c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K > (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 > ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.