Full_Name: Martha Nason Version: 2.0.1 OS: Windows XP Submission from: (NULL) (137.187.154.154)
I am running simulations using fisher's test on 2 x c tables and a very small p.value from fisher's test (<2.2e-16) is returned as a negative number. Code follows. > set.seed(0) > nreps.outer <-7 > pvalue.fisher <- rep(NA,nreps.outer) > > population1 <- c( rep("A",300),seq(1:100)) > > population2 <- c( rep("A",100),seq(101:200)) > > > for (j in 1:nreps.outer){ + n1 <- sample(30:100,1) + n2 <- sample(30:100,1) + + group1 <- sample(population1, n1, replace=T) + group2 <- sample(population2, n2, replace=T) + + pvalue.fisher[j] <- fisher.test(table(c(group1,group2),c(rep("group1",n1),rep("group2",n2))))$p.value + + print(c(j,pvalue.fisher[j])) + + } [1] 1.000000e+00 3.581362e-05 [1] 2.0000000 0.1424779 [1] 3.0000000 0.1196600 [1] 4.000000000 0.004222897 [1] 5.000000e+00 3.234016e-07 [1] 6.000000000 0.003240286 [1] 7.000000e+00 -3.847298e-05 > > fisher.test(table(c(group1,group2),c(rep("group1",n1),rep("group2",n2)))) Fisher's Exact Test for Count Data data: table(c(group1, group2), c(rep("group1", n1), rep("group2", n2))) p-value < 2.2e-16 alternative hypothesis: two.sided > fisher.test(table(c(group1,group2),c(rep("group1",n1),rep("group2",n2))))$p.value [1] -3.847298e-05 ______________________________________________ R-devel@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-devel