[R] t.test() with missing values

[Petr PIKAL]

> Petr PIKAL wrote:
> > Hi
> >
> > r-help-bounces at r-project.org napsal dne 14.09.2007 13:50:58:
> >
> > 
> >> Birgit Lemcke wrote:
> >> 
> >>> Am 14.09.2007 um 12:05 schrieb Peter Dalgaard:
> >>>
> >>> 
> >>>> S Ellison wrote:
> >>>> 
> >>>>>>>> Peter Dalgaard <P.Dalgaard at biostat.ku.dk> 14/09/2007 09:26:16 
>>>
> >>>>>>>>
> >>>>>>>> 
> >
> >
> > <snip>
> >
> >
> > 
> >>>> Yes, but....
> >>>>
> >>>> I don't think lme() will do better than what you can do by hand: 
Get 
> >>>> 
> > two
> > 
> >>>> independent estimates of mu1-mu2 (one estimate from the pairs and 
one
> >>>> from the singlets), compute a weighted average using the s.e.'s and 

> >>>> 
> > test
> > 
> >>>> that against zero (possibly after testing them for equality for 
good
> >>>> measure). This is easy if you use a plug-in approach: first assume 
> >>>> 
> > that
> > 
> >>>> the s.e. are known, then plug in their empirical value. The tricky 
> >>>> 
> > bit
> > 
> >>>> is to calculate the DF in the style of Welch's test.
> >>>> 
> >>>             I apologise but I really can not follow your 
explanations.
> >>> I am  R and Stastistics Beginner.
> >>>
> >>>             What do you mean with mu1-mu2 and what are s.e.´s?
> >>>
> >>> 
> >> That was a reply to S. Ellison. If you don't understand it, don't 
worry;
> >> you'll probably need to read a book chapter or more about weighted
> >> analyses to get up to speed for that. 
> >>
> >> mu1, mu2 : (theoretical) mean for group 1, 2
> >> s.e.: standard error
> >> 
> >
> > But as Birgit actually does not have any paired values, according to 
the 
> > data she had sent, she can not do paired t.test at all. The only way 
is to 
> > compare averages from each vector by non paired t.test or to get some 
new 
> > values for which she have counterparts. 
> > 
> True, for that particular set of data. I did make that point in my first
> reply (tried to, anyways), but I didn't repeat it the second time.
> 
> If you look back, you'll see that Birgit was also doing
> 
> TTest75<-t.test(Fem75, Mal75, alternative= "two.sided", paired= TRUE)
> 
> and presumably there are several similar sets of data. This "works" in 
the 
> sense that it produces a test, but one could get the suspicion that it 
is only
> using a small subset of available data if the dropout rate is 
approaching that
> of Fem66/Mal66. Hence the discussion of the general case.

I see, sorry I did not noticed before. But everything depends on which 
hypotheses she wants to test. She told us about 334 different plant 
species (male and female) and if she wants to test if male and female is 
different she does not have many other options. 

Petr

> 
> > Regards
> > Petr
> >
> >
> >
> > 
> >>>             Once again thank you for your help.
> >>>
> >>>             Birgit
> >>>
> >>>
> >>>
> >>>
> >>> 
> >>>> --   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
> >>>>
> >>>>
> >>>> 
> >>> Birgit Lemcke
> >>> Institut für Systematische Botanik
> >>> Zollikerstrasse 107
> >>> CH-8008 Zürich
> >>> Switzerland
> >>> Ph: +41 (0)44 634 8351
> >>> birgit.lemcke at systbot.uzh.ch
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>> 
> >> -- 
> >>    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
> > 
> >> ______________________________________________
> >> R-help at r-project.org 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 at r-project.org 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             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
> 
> ______________________________________________
> R-help at r-project.org 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.