Silent failure with NA results in fligner.test()

On Jan 24, 2021, at 6:52 PM, Kurt Hornik <Kurt.Hornik at wu.ac.at> wrote:

Karolis K writes:

To me it seems like returning chi-sq = 0 and p-value = 1 would make sense.
It would also be consistent with other scenarios of equal variance in all
groups. One example:

fligner.test(1:8, gl(2,4))
#        Fligner-Killeen test of homogeneity of variances
#
# data:  1:8 and gl(2, 4)
# Fligner-Killeen:med chi-squared = 0, df = 1, p-value = 1

But I am aware that other tests implemented in stats:: sometimes throw
errors in similar situations.

Maybe someone more familiar with the behaviour and philosophy behind
stats:: preferences can add more weight here?

Thanks for spotting this.  After some internal discussions, we've come
to the conclusion that there is no "obvious" way to handle situations
where the Fligner-Killeen:med chi-squared test statistic is undefined
(i.e., when the denominator is zero).  [Owing to the discreteness of the
ranks, trying to take limits will not work.]  For now, these
sitatuations consistently give NaN/NA instead of errors (and the numeric
computations were improved so that it should no longer possible to get a
zero denominator and a non-zero numerator).

Best
-k

Warm regards,
Karolis K.

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