On Apr 20, 2011, at 21:30 , Fay, Michael (NIH/NIAID) [E] wrote: > Hi, > > I received a bug report for my exact2x2 package that seems to apply to > fisher.test in the stats package also. > > Here is some code which creates the error: > >> x<-factor(c(0,1,1),levels=c(0,1)) >> y<-factor(c(1,1,1),levels=c(0,1)) >> fisher.test(x,y) > Error in fisher.test(x, y) : 'x' and 'y' must have at least 2 levels >> > > The help says that x and y could be factors, and technically y does have 2 > levels, although both are not observed. There is no problem statistically > with y not having 2 observed levels, and > >> fisher.test(table(x,y)) > > Produces the correct p-value of 1 and no errors. > > There is an easy solution. In fisher.test replace > > x <- factor(x[OK]) > y <- factor(y[OK]) > > > with > > x <- as.factor(x[OK]) > y <- as.factor(y[OK]) > > (similar to how it is done in mcnemar.test). > >
OK. Of course, the test makes little sense statistically either way if one factor has only one level used, but I can imagine that a p value of 1 is preferable to an error, and the consistency is probably worth having too. Fixed in r-devel. -- Peter Dalgaard Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd....@cbs.dk Priv: pda...@gmail.com ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
