How to handle missing values

[Richard Eckart de Castilho]

Hi,

I am using the Krippendorff's Alpha (nominal) from DKPro Statistics as it apparently can handle missing values.

I guess it is somehow clear how the measure should handle these cases:

Rater 1 | Rater 2
--------+--------
CAT X | CAT X
CAT X | CAT Y
CAT Y | CAT X
CAT X | null
CAT Y | null
null | CAT X
null | CAT Y

but what about

Rater 1 | Rater 2
--------+--------
null | null

Does it sensibly handle such cases or should such cases not even be added to the study in the first place?

Cheers,

-- Richard