Re: st: running marginsplots without rerunning margins again

[jpitblado@stata.com (Jeff Pitblado, StataCorp LP)]

Doug Hess <douglasrhess@gmail.com> is using -margins- and -marginsplot-, and
has some questions about working with -margins- results.

> I just installed Stata 12 and am playing with the "marginsplot"
> command. I am wondering how to run margins plot on a restored margins?
> Can it? Complex margins commands can take a long time to run. Is there
> a way to restore or use saved results from a complex running of
> margins so that I can fiddle with the graph later?
> 
> Come to think of it, how do I redisplay results from a margins command
> after "restoring" a stored file or "using" a saved file. For
> regression estimates you just type regress and it shows it. How is
> this done for other saved files.

Scott Merryman <scott.merryman@gmail.com> mentioned using -_return hold- and
-_return restore- which solved Doug's orginial question.

Richard Williams <richardwilliams.ndu@gmail.com> also had a solution, but it
didn't work as expected.

> I thought it would simply be a matter of using the -post- option of 
> margins and the -est store- and -est restore- commands. To my 
> surprise, though, the following produces an error at the end:
> 
> clear all
> sysuse auto
> reg  price mpg i.foreign
> margins foreign, post
> est store margins1
> marginsplot
> reg  price mpg i.foreign  weight
> est restore margins1
> margins
> marginsplot
> 
> The error is "previous command was not margins." But if you do 
> -ereturn list-, it does say the last command was -margins-. I am 
> surprised it doesn't work, and I wonder if this is a bug or if there 
> is some good reason for this.

We agree with Richard on this and plan to make -marginsplot- recognize the
-e()- results posted by -margins, post- in a future ado-file update.

Later in the thread, Richard wrote:

> Personally, my wish would be (for Stata 12.1?) that when you use the -post-
> option on -margins-, you would be able to use the ereturned results the same
> way as you can with any estimation command. e.g. replay them, save them,
> restore them, run post-estimation commands after restoring. I can't think of
> another command that requires you to store or save the returned results as
> well. 

We are not sure which features Richard feels are missing.

When the -post- opton is used with -margins-, the following standard
estimation command features are also available for -margins-:

	* replay -margins- results
	* -estimates store- and -estimates restore- works
	* -estimates save- and -estimates use- works
	* -test-, -lincom-, -testnl-, -nlcom-, and all other standard
	  postestimation commands work with the posted -margins- results

The following example works in Stata 11 and Stata 12:

Load some data:

	. sysuse auto

Fit a model, compute some margins with -post-, and store the margins results:

	. regress mpg i.foreign
	. margins for, post
	. est store margins1

Do it again with a different model:

	. regress mpg i.rep78
	. margins rep, post
	. est store margins2

Restore the first set of -margins- results, replay them, then use -test-:

	. est restore margins1
	. margins
	. test 0.for = 1.for

--Jeff
jpitblado@stata.com
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/