[R] Randomization tests, grouped data

Tom Backer Johnsen backer at psych.uib.no
Sat Jan 12 08:31:11 CET 2008

Johannes Hüsing wrote:
> Tom Backer Johnsen <backer at psych.uib.no> [Fri, Jan 11, 2008 at 06:57:41PM CET]:
> [...]
>>> Are there something that can handle this in R?
> Have you considered the coin package? 

I'll have a look at it.
>> After a few hours thinking on and off about the problem, I suspect 
>> that the question may be stupid or silly (or both).  If that is the 
>> case, I would very much like to know why.
> I am not quite clear in my thinking anymore, but there are 2^2n 
> permutations, of which (2n choose n) happen to yield the same 
> effect. These cases are "part of life" and should be counted in
> the permutation test just as well. You might save a little bit of
> computation time by singling these group-preserving permutations
> out, but this is not worth the while at all. '

Sure, but the question is simply:  Do the permutations that only 
shuffle things within groups introduce some kind of a bias?  I have a 
feeling that this is worse if the groups are not equally large.


| Tom Backer Johnsen, Psychometrics Unit,  Faculty of Psychology |
| University of Bergen, Christies gt. 12, N-5015 Bergen,  NORWAY |
| Tel : +47-5558-9185                        Fax : +47-5558-9879 |
| Email : backer at psych.uib.no    URL : http://www.galton.uib.no/ |

More information about the R-help mailing list