[R] test for equal distributions with small numbes of observations
kjetil brinchmann halvorsen
kjetil at entelnet.bo
Wed Aug 20 04:49:35 CEST 2003
On 19 Aug 2003 at 10:15, Christoph Lehmann wrote:
> Dear R-pros
>
> I have a problem, for which usually I would apply a chisq.test or a
> fisher.test:
>
try
?chisq.test
which tells you you can say
chisq.test(..., sim=TRUE, B=20000)
and the simulation will be very fast!
Kjetil Halvorsen
>
>
> 40 objects, each given either a "0" or "1", regarding if this object
> later on will be remembered by a subject or not.
>
> 7 subjects investigated
>
> means: we have a 2x40 matrix, each cell the number of subjects for who
> the object i has been given either "0" or "1" e.g.
>
> objects:
> 1 1 3 39 40
> ------------------------------------------
> "0" 1 2 2 .. 7 7
> "1" 4 4 5 .. 0 0
>
> over all 40 objects, we have 67% of "1" and 33% of "0"
>
> I want to know, if for the 40 objects, the ratio of "0"/"1" differs or
> not, i.e. if they have the same distribution.
>
> I cannot use a chisq.test since the expected frequencies are < 5 for the
> "0" cells.
>
> Fisher.test seems to run for > 12h on a PIV 1.8GHz...
>
> what do you recommend me to do?
>
> Many thanks
>
> Christoph
> --
> > recognition
> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] [,14]
> [1,] 1 2 2 2 2 3 3 3 3 3 3 3 4 4
> [2,] 4 4 5 4 4 3 4 4 4 4 3 4 3 3
> [,15] [,16] [,17] [,18] [,19] [,20] [,21] [,22] [,23] [,24] [,25] [,26]
> [1,] 4 4 4 4 4 4 5 5 5 5 5 5
> [2,] 3 2 3 3 2 3 2 2 2 2 2 2
> [,27] [,28] [,29] [,30] [,31] [,32] [,33] [,34] [,35] [,36] [,37] [,38]
> [1,] 5 5 5 5 5 6 6 6 6 6 6 6
> [2,] 2 2 2 2 2 1 1 1 1 1 1 1
> [,39] [,40]
> [1,] 7 7
> [2,] 0 0
>
> > fisher.test(recognition)
>
>
> --
> Christoph Lehmann <christoph.lehmann at gmx.ch>
>
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