c.test</code> is used when <code>y</code> is numeric, and
<code>factor.test</code> is used in all other instances.</p>
<p>Specifically, these functions should take only <code>x</code>,
<code>y</code>, and <code>w=NULL</code> as arguments, and should return
a list with three elements: the name of the test statistic, the test
statistic itself, and the p-value of the test.</p>
<p>By default, these are the internal functions
<code>vtable:::chisq.it</code> for <code>factor.test</code> and
<code>vtable:::groupf.i