
Am 14.09.2007 um 10:26 schrieb Peter Dalgaard:

> Birgit Lemcke wrote:
>> Thanks for your answer.
>>
>> First I will show you both vectors:
>>   [...]
>>
>> I tried this (complete.cases(Fem66, Mal66)) and you are right, it
>> gives me back:
>>
>> (complete.cases(Fem66, Mal66))
>>   [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
>> FALSE FALSE FALSE
> [....]
>> I thought the t.test is a comparison of means and why can I not  
>> use it
>> if I have a lot of missing values. Is the reason that I use the  
>> paired
>> option?
>> What is different in the calculation using paired?
>>
>> Ah ja this seems to be the case:
>>
>> T66<-t.test(Mal66, Fem66, alternative= "two.sided")
>>> T66
>>
>>
>> Welch Two Sample t-test
>>
>> data:  Mal66 and Fem66
>> t = -0.4881, df = 49.229, p-value = 0.6277
>> alternative hypothesis: true difference in means is not equal to 0
>> 95 percent confidence interval:
>> -1.4637045  0.8915906
>> sample estimates:
>> mean of x mean of y
>> 5.096552  5.382609
>>
>> I use the paired option because may plants (male and female)  
>> belong to
>> the same species (and because may boss said that I have to use paired
>> in this case)
> Don't do what your boss says, do what is right! (It might of course be
> the same thing). So pair #1 is one species, pair #2 another  
> species, up
> to 331 different species?
>
	348 species. The rest is correct.
>> So what can I do now to solve my problem?
>>
>> Do you think I should not use paired=TRUE?
> You *can* only use it when you have pairs, and you must do it then, to
> correct for intra-pair correlation. The drawback is that it looks only
> at complete pairs, throwing away all the singlets. It is possible to
> recover the information from the singlets , basically by combining a
> paired test for the pairs and an unpaired one for the singlets.  
> (Someone
> must have written this down, but I'm afraid I don't have a nice  
> reference).

	Anyway, thanks a lot and I will try to find it or perhaps somebody  
else in the mailing list knows anything about it.
>
> -- 
>    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@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@systbot.uzh.ch






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