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| From | Maarten Buis <maartenlbuis@gmail.com> |
| To | statalist@hsphsun2.harvard.edu |
| Subject | Re: st: random quadratic effect without random linear effect? |
| Date | Thu, 20 Jun 2013 09:36:30 +0200 |
On Thu, Jun 20, 2013 at 12:07 AM, Jordan Silberman wrote: > For a model run in xtmixed, we all know that if you include a fixed > quadratic effect of predictor A, then you typically should include the > lower order fixed linear effect of A as well. > > Does an analogous rule apply to random effects? I think that it may > make theoretical sense to include only a random quadratic effect, > without the corresponding random linear effect. Can anyone tell me > whether or not this would be "kosher?" That obviously depends on your argument. As long as your can give a reasonable argument for your choices everything is allowed. However, what you propose is unusual, so you'd better have a good argument because when you try to publish this someone is guaranteed to ask you about it. Moreover, I find it hard to imagine an argument that could support such a model, so I suspect that there is an error in your argument. But this is just a guess based on very limited information. This is all we can say, since you did not give us your argument. -- Maarten --------------------------------- Maarten L. Buis WZB Reichpietschufer 50 10785 Berlin Germany http://www.maartenbuis.nl --------------------------------- * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/