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st: RE: test difference of two linear combinations that are differences of means
From
"Schaffer, Mark E" <[email protected]>
To
"[email protected]" <[email protected]>
Subject
st: RE: test difference of two linear combinations that are differences of means
Date
Fri, 7 Feb 2014 10:34:17 +0000
David,
> -----Original Message-----
> From: [email protected] [mailto:owner-
> [email protected]] On Behalf Of Radwin, David
> Sent: 06 February 2014 21:03
> To: [email protected]
> Subject: st: test difference of two linear combinations that are differences of
> means
>
>
> Dear Statalisters,
>
> How do I test whether the difference of two linear combinations is statistically
> significant if the linear combinations are differences of means?
>
> In the contrived example below, I want to test whether the 0.08 absolute mean
> difference between the South and West in mean January temperatures is
> different than the 8.88 absolute mean difference between the South and West
> in July temperatures.
>
> I can't use -suest- as some earlier posts have suggested because I get the error
> message, "impossible to retrieve e(b) and e(V) in A" (error 198).
-suest- works after -regress- (among other commands). Can you rejig your example so that the means are estimated by -regress- and reported as coefficients? E.g., instead of
mean tempjan, over(region)
use
reg tempjan ibn.region, nocons
HTH,
Mark
>
> David
> --
> David Radwin, Senior Research Associate
> Education and Workforce Development
> RTI International
> 2150 Shattuck Ave. Suite 800, Berkeley, CA 94704
> Phone: 510-665-8274
>
> www.rti.org/education
>
> . sysuse citytemp, clear
> (City Temperature Data)
>
> . mean tempjan, over(region)
>
> Mean estimation Number of obs = 954
>
> NE: region = NE
> _subpop_2: region = N Cntrl
> South: region = South
> West: region = West
>
> --------------------------------------------------------------
> Over | Mean Std. Err. [95% Conf. Interval]
> -------------+------------------------------------------------
> tempjan |
> NE | 27.88537 .2766693 27.34241 28.42832
> _subpop_2 | 21.69437 .3397395 21.02764 22.36109
> South | 46.1456 .6568972 44.85647 47.43473
> West | 46.22539 .7033823 44.84503 47.60575
> --------------------------------------------------------------
>
> . lincom [tempjan]West - [tempjan]South
>
> ( 1) - [tempjan]South + [tempjan]West = 0
>
> ------------------------------------------------------------------------
> ------
> Mean | Coef. Std. Err. t P>|t| [95% Conf.
> Interval]
> -------------+----------------------------------------------------------
> ------
> (1) | .0797906 .9624243 0.08 0.934 -1.808925
> 1.968506
> ------------------------------------------------------------------------
> ------
>
> . mean tempjuly, over(region)
>
> Mean estimation Number of obs = 954
>
> NE: region = NE
> _subpop_2: region = N Cntrl
> South: region = South
> West: region = West
>
> --------------------------------------------------------------
> Over | Mean Std. Err. [95% Conf. Interval]
> -------------+------------------------------------------------
> tempjuly |
> NE | 73.35 .1843789 72.98816 73.71184
> _subpop_2 | 73.46725 .1841403 73.10589 73.82862
> South | 80.9896 .1881789 80.62031 81.35889
> West | 72.10859 .4051957 71.31342 72.90377
> --------------------------------------------------------------
>
> . lincom [tempjuly]West - [tempjuly]South
>
> ( 1) - [tempjuly]South + [tempjuly]West = 0
>
> ------------------------------------------------------------------------
> ------
> Mean | Coef. Std. Err. t P>|t| [95% Conf.
> Interval]
> -------------+----------------------------------------------------------
> ------
> (1) | -8.881006 .4467604 -19.88 0.000 -9.757754
> -8.004258
> ------------------------------------------------------------------------
> ------
-----
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