[R] in cor.test, difference between exact=FALSE and exact=NULL
P.Dalgaard at biostat.ku.dk
Fri Aug 31 17:06:11 CEST 2007
Andrew Yee wrote:
> Pardon my ignorance, but is there a difference in cor.test between
> exact=FALSE and exact=NULL when method=spearman?
> Take for example:
> cor.test(x,y, method="spearman", exact=NULL)
> This gives an error message,
> Warning message: Cannot compute exact p-values with ties in:
> cor.test.default(x, y, method = "spearman", exact = NULL)
> However, when exact is changed to FALSE, this seems to run okay.
> cor.test(x,y, method="spearman", exact=FALSE)
> Question: should this be exact = FALSE in the documentation and/or the code?
No. The default is indeed NULL.
This implies that calculation of exact p-values will be attempted, and
when there are ties you get a warning (NB: not error) message. Setting
exact=FALSE, no attempt is made and no warning is given.
> MGH Cancer Center
> R-help at stat.math.ethz.ch mailing list
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
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