statistics.compare: a group has zero varianc...

Warnings reference › compare:zero-variance

Identifier

compare:zero-variance

Raised by

The grid (core)

Since

1.106.0

What happened

Every value in one group is identical, so its variance is zero and the statistic the test divides by is undefined. The call returns null rather than report a p-value from a degenerate sample.

The fix

Check that the measure actually varies within each group, or drop the constant group.

Reference

Covered in full at the API reference.