Zero alteration and mixed models?

Ben Bolker · 2014-05-10T19:26:30Z

Kirsty Gurney writes: > > Good afternoon; > > A non-R specific question about mixed models, but I am sending this email > with the hope that others in this group may be familiar with zero-altered > (i.e. zero-inflated or hurdle) models in a mixed model context. I'll take at a stab at this with the usual caveat that the advice is worth whatever you paid for it :-) > My current project is focused on understanding changes in wetland biota > related to environmental chang

Ben Bolker

Sat, May 10, 2014 12:26 PM

Kirsty Gurney <kegurney at ...> writes:

I'll take at a stab at this with the usual caveat that the advice
is worth whatever you paid for it :-)

I think the answer to this question depends on your general purpose
in modeling, and your general philosophy of model selection.  In other
words, the answer is similar to the question of whether you should
drop or simplify any terms that don't appear to be doing anything useful.

  If you are doing confirmatory hypothesis testing, then you definitely
shouldn't.

  If you are primarily interested in prediction, it might be
reasonable to try to do some form of model selection, which will
generally increase the bias and decrease the variance (with due
attention to the effect of model uncertainty and model selection on
the confidence intervals/uncertainty of the estimates and predictions).
What you're describing above is essentially a crude form of backward
stepwise model selection (or at least the first step ...)

  Ben Bolker

Zero alteration and mixed models?

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