[R] t.test() with missing values

[Peter Dalgaard]

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.

> 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