[R] fisher.test - FEXACT error 7
Bernardo Rangel Tura
tura at centroin.com.br
Mon Mar 23 11:25:52 CET 2009
On Fri, 2009-03-20 at 18:29 +0000, Helena Mouriño wrote:
> Dear all,
> Im having an awkward problem in R. When I write the command
> Fisher.test(school.data,workspace=2e+07), where school.data is the matrix
> corresponding to the data set,
> I get the error message:
> FEXACT error 7.
> LDSTP is too small for this problem.
> Try increasing the size of the workspace.
> Increasing the workspace:
> I get a different message, but it still doesnt work:
> NAs in foreign function call (arg 10)
> In addition: Warning message:
> In fisher.test(dados, workspace = 1e+10, alternative = "two.sided") :
> NAs introduced by coercion
In this case you can try 3 solutions:
1- chisq.test(school.data), but pay attention if expected value of any
cell is < 5
2- Fisher.test(school.data,workspace=2e+07,hybrid=TRUE) from Help
For larger than 2 by 2 tables and 'hybrid = TRUE', asymptotic
chi-squared probabilities are only used if the 'Cochran
conditions' are satisfied, that is if no cell has count zero, and
more than 80% of the cells have counts at least 5.
3- Use "large tables" approach from Sir David Cox:
Law, G. R. and Cox, D. R. and Machonochie, N. E. S. and Simpson, J. and
Roman, E. and Carpenter, L. M. (2001) Large tables. Biostatistics
Bernardo Rangel Tura, M.D,MPH,Ph.D
National Institute of Cardiology
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