Anthony,
I would definitely recommend looking at the official release MI commands.
I also don't think that 4 imputations is anywhere near enough. Unless
there's something extraordinarily odd about your dataset or computer,
it should be able to cope with many more imputations. That said, with
longitudinal data developing a reasonable imputation model is not an
easy task. You often need to handle time quite carefully to ensure
that trends don't become too strange, for instance, and be very sure
you've done a thorough outlier screening.
Jay
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