1) Which specification approach A or B is the correct
(or better) one?
Or, more generally, should all factor variables be "noms=" and all
ordered factors be "ords="?
My rule of thumb is that if you use an analytical technique that
treats the variable as normally distributed continuous, impute as
continuous. If you use an analytical approach that treats the data as
ordinal you can only impute as ordinal as a fraction will not be
interpretable for your analytical model.
As for the second problem, I have no idea. But I know Amelia (along
with all the other imputation methods I've seen) likes a very large
sample size. If you are using a subset that is too small, that might
be part of your problem. I'd give it a try with all the data just to
see if it runs.
HTH
L
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