st: RE: RE: test difference of two linear combinations that are differences of means

["Radwin, David" <dradwin@rti.org>]

Mark,

Thank you. That worked great. I appreciate your help.

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

> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-
> statalist@hsphsun2.harvard.edu] On Behalf Of Schaffer, Mark E
> Sent: Friday, February 07, 2014 2:34 AM
> To: statalist@hsphsun2.harvard.edu
> Subject: st: RE: test difference of two linear combinations that are
> differences of means
> 
> David,
> 
> > -----Original Message-----
> > From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-
> > statalist@hsphsun2.harvard.edu] On Behalf Of Radwin, David
> > Sent: 06 February 2014 21:03
> > To: statalist@hsphsun2.harvard.edu
> > 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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