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RE: st: nonfactorial combinations with -margins-
From
Richard Williams <[email protected]>
To
[email protected], "[email protected]" <[email protected]>
Subject
RE: st: nonfactorial combinations with -margins-
Date
Thu, 01 Aug 2013 15:48:50 -0500
At 02:09 PM 8/1/2013, Feiveson, Alan H. (JSC-SK311) wrote:
Rich - That's it! Didn't know the "at" could be repeated.
It does say in the documentation that "Multiple at() options can be
specified, and each will produce a different set of margins." But,
the documentation for margins is so huge that it is easy to miss
things! I actually just guessed at the syntax and found the docs afterwards.
Thanks.
Al
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Richard Williams
Sent: Thursday, August 01, 2013 3:02 PM
To: [email protected]; [email protected]
Subject: Re: st: nonfactorial combinations with -margins-
What is with the numbers on at1 and at2? Is this what you want?
margins, at(headroom = 2.4 weight = 2000 length = 150 ) at(headroom =
3.6 weight = 3000 length = 200 )
At 01:29 PM 8/1/2013, Feiveson, Alan H. (JSC-SK311) wrote:
>Hi - In Stata 13, I've been struggling with getting -margins- to
>produce arbitrary combinations of several predictors without creating a
>huge list of all possible combinations.
>
>
>Example:
>
>. sysuse auto,clear
>(1978 Automobile Data)
>
>. reg price headroom weight length
>
> Source | SS df MS Number of
> obs = 74
>-------------+------------------------------ F( 3,
70) = 13.23
> Model | 229789847 3 76596615.8 Prob >
> F = 0.0000
> Residual
> | 405275549 70 5789650.7 R-squared = 0.3618
>-------------+------------------------------ Adj
R-squared = 0.3345
> Total | 635065396 73 8699525.97 Root
> MSE = 2406.2
>
>-------------------------------------------------------------------
-----------
> price | Coef. Std. Err. t P>|t| [95%
> Conf. Interval]
>-------------+---------------------------------------------------------
>-------------+-------
> headroom
> | -486.4429 388.7626 -1.25 0.215 -1261.806 288.9197
> weight
> | 4.674047 1.118074 4.18 0.000 2.444119 6.903975
> length
> | -87.59202 39.88962 -2.20 0.031 -167.1494 -8.034676
> _cons
> | 9969.584 4304.018 2.32 0.023 1385.49 18553.68
>-----------------------------------------------------------------------
>-------
>
>
>
>
>Suppose I want to get predictions at only two combinations of these
>three predictors:(headroom = 2.4, weight = 2000, length = 150) and
>(headroom = 3.6, weight = 3000, length = 200). But if I specify
>
>
>. margins,at(headroom = (2.4 3.6) weight = (2000 3000) length = (150
>200) )
>
>Adjusted predictions Number of
obs = 74
>Model VCE : OLS
>
>Expression : Linear prediction, predict()
>
>1._at : headroom = 2.4
> weight = 2000
> length = 150
>
>2._at : headroom = 2.4
> weight = 2000
> length = 200
>
>3._at : headroom = 2.4
> weight = 3000
> length = 150
>
>4._at : headroom = 2.4
> weight = 3000
> length = 200
>
>5._at : headroom = 3.6
> weight = 2000
> length = 150
>
>6._at : headroom = 3.6
> weight = 2000
> length = 200
>
>7._at : headroom = 3.6
> weight = 3000
> length = 150
>
>8._at : headroom = 3.6
> weight = 3000
> length = 200
>
>-------------------------------------------------------------------
-----------
> | Delta-method
> | Margin Std. Err. t P>|t| [95%
> Conf. Interval]
>-------------+---------------------------------------------------------
>-------------+-------
> _at |
> 1 | 5011.412 616.6852 8.13 0.000 3781.473
> 6241.352
> 2 | 631.8115 1654.47 0.38 0.704 -2667.925
> 3931.548
> 3 | 9685.46 1488.435 6.51 0.000 6716.87
> 12654.05
> 4 | 5305.859 655.2722 8.10 0.000 3998.959
> 6612.758
> 5 | 4427.681 810.5569 5.46 0.000 2811.076
> 6044.286
> 6 | 48.0801 1620.927 0.03 0.976 -3184.757
> 3280.917
> 7 | 9101.728 1584.549 5.74 0.000 5941.445
> 12262.01
> 8 | 4722.127 581.5246 8.12 0.000 3562.313
> 5881.941
>-----------------------------------------------------------------------
>-------
>
>
>
>I get all 8 combinations of these three variables at two values each,
>yet I only care about two of them. Clearly this can get out of hand if
>there are lots of predictors or values in these lists.
>
>
>What I would like is something like
>
>. margins,at1(headroom = 2.4 weight = 2000 length = 150 ) at2(headroom
>= 3.6 weight = 3000 length = 200 )
>
>
>but this is not allowed.
>
>Is there a syntax for doing what I want that I have overlooked?
>
>Thanks
>
>
>Al Feiveson
>
>
>*
>* 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/
-------------------------------------------
Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
HOME: (574)289-5227
EMAIL: [email protected]
WWW: http://www.nd.edu/~rwilliam
*
* 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/
*
* 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/
-------------------------------------------
Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
HOME: (574)289-5227
EMAIL: [email protected]
WWW: http://www.nd.edu/~rwilliam
*
* 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/