Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: st: Testing whether two estimated survey means are statistically different
From
Nick Winter <[email protected]>
To
[email protected]
Subject
Re: st: Testing whether two estimated survey means are statistically different
Date
Thu, 20 Oct 2011 10:43:55 -0400
Ah yes, I stand corrected.
Nick
On 10/20/2011 10:39 AM, Austin Nichols wrote:
Nick--
The poster (Andrew Wade) has survey data, though.
In survey data, using a cluster-robust variance estimator, the two are
identical.
webuse nhanes2, clear
svy: reg bpsystol black, sformat(%7.6f)
qui svy: mean bpsystol, over(black)
lincom _b[1]-_b[0], sformat(%7.6f)
On Thu, Oct 20, 2011 at 10:00 AM, Nick Winter<[email protected]> wrote:
There is a subtle difference between -svy: reg- and -svy: mean- followed by
-lincom-. The former corresponds to a t-test with the assumption that the
variances in the two populations are equal; the latter corresponds (almost
exactly) to a t-test without that assumption. The "almost exactly" is due
to a difference in calculation of degrees of freedom.
Leaving aside -svy-, we can see the slightly different standard errors:
sysuse auto
reg mpg foreign
ttest mpg, over(foreign)
mean: mpg, over(foreign)
lincom _b[Domestic]-_b[Foreign]
ttest mpg, over(foreign) unequal
- Nick Winter
On 10/20/2011 4:58 AM, Maarten Buis wrote:
On Wed, Oct 19, 2011 at 11:33 PM, Andrew Wade<[email protected]>
wrote:
Presumably the regression approach, where you have a single dummy for the
sub-population, will be identical (or near identical) to:
- estimating svy: mean with over command (ie. mean for sub-population,
and not in sub-population).
- lincom after svy: mean.
*
* 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/
--
--------------------------------------------------------------
Nicholas Winter 434.924.6994 t
Associate Professor 434.924.3359 f
Department of Politics [email protected] e
University of Virginia faculty.virginia.edu/nwinter w
S385 Gibson Hall, South Lawn
*
* 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/