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# RE: st: marginsplot after xtmixed with square term

 From "Sun, Wensheng" To "statalist@hsphsun2.harvard.edu" Subject RE: st: marginsplot after xtmixed with square term Date Wed, 13 Mar 2013 20:55:23 -0500

```Hi Scott,

It works. By the way, could you explain what "i.pressure c.repl##c.repl##i.pressure" means?

Thank you very much!

Wensheng

________________________________________
From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] On Behalf Of Scott Merryman [scott.merryman@gmail.com]
Sent: Wednesday, March 13, 2013 8:09 PM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: marginsplot after xtmixed with square term

Stata does not know that repl2 is the square of repl.

Try:

webuse acmemanuf
lowess y repl, by(pressure)
//gen repl2=repl^2
gen id=.
replace id=temp if pressure==1
replace id=temp+3 if pressure==2
replace pressure=0 if pressure==1
replace pressure=1 if pressure==2
xtmixed y  i.pressure c.repl##c.repl##i.pressure  || id: repl,
cov(uns) res(ind) mle variance
margins pressure, at(repl=(1(1)10))
marginsplot

Scott

On Wed, Mar 13, 2013 at 12:43 PM, Sun, Wensheng <wsun@bcm.edu> wrote:
> webuse acmemanuf
> lowess y repl, by(pressure)
> gen repl2=repl^2
> gen id=.
> replace id=temp if pressure==1
> replace id=temp+3 if pressure==2
> replace pressure=0 if pressure==1
> replace pressure=1 if pressure==2
> xtmixed y c.repl## i.pressure c.repl2##i.pressure  || id: repl, cov(uns) res(ind) mle variance
> margins pressure, at(repl=(1(1)10))
> marginsplot
>
> I expected to get concaved curves from marginsplot like I usually got from modeling estimates with square terms; however, what I got here were two straight lines. Please help me to fix my codes.
>
> Thank you very much!
>
> Wensheng
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```