[R] Kendall's tau

Jonathan Baron baron at cattell.psych.upenn.edu
Thu Apr 25 12:04:13 CEST 2002

On 04/25/02 05:20, Martin Henry H. Stevens wrote:
>A search of the archives did not reveal an answer:
>For basic tests of association, where one has no a priori knowledge of the 
>form of the relation or of the distributions of the variables, rank 
>correlation seems like a good start. Why is cor.test() with Kendall and 
>Spearman options relegated to the ctest package, rather than in the base 
>package? Does this suggest that the developers consider other tests of 
>association more generally useful?

I think I remember a version of R in which the ctest package had
to be loaded with library(), but it was a long time ago.
Everything in the ctest package is now simply available when you
start R.  I suspect that it is separate from "base" for
historical reasons.  It isn't clear to me whether change is
needed, and, if so, whether the base package should become even
larger or whether it should be broken up into yet more parts.  As
things are now, even on a fast computer loading from its own
disk, the html listing of the base package takes a bit of time to
load.  My own opinion is that this is a low-priority issue.

As for what to do when you don't know what your data look like,
my own recommendation is not to do anything in cor.test(), but,
use plot(), and then figure out what to do next, e.g., fix
errors, apply a tranform, or do a test.  Sometimes, of course,
you know in advance that tau is the appropriate test.

Jonathan Baron, Professor of Psychology, University of Pennsylvania
Home page: http://www.sas.upenn.edu/~baron
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