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Re: st: stumped with lincom after svymean


From   <hk489@nyu.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: stumped with lincom after svymean
Date   Tue, 31 Aug 2004 17:04:54 -0400

Hi Jeff and other Listers -

How about the question 2 of Robert? Below is the question:

>2 - Is it possible to estimate a one-way anova to detect group differences 
> with svy commands in Stata 8 based on my above example?

In Robert's example, variable x has three categories: 0, 1, and 2. Is there any way to compare the three group differences concurrently (like a one-way anova) with svy commands? 


Hong



----- Original Message -----
From: jpitblado@stata.com (Jeff Pitblado, StataCorp LP)
Date: Tuesday, August 31, 2004 12:16 pm
Subject: Re: st: stumped with lincom after svymean

> "Robert Bozick" <robertbozick@hotmail.com> asks about using -test- 
> after-svymean, by()-:
> 
> > Here is what I am trying to accomplish.  I have a continuous 
> variable y, and 
> > a categorical variable x.  The categorical variable x has three 
> categories: 
> > 0, 1, and 2.  I want to test whether y is different among the 
> categories of 
> > my variable x.  My data are collected using a stratfied, cluster 
> design and 
> > therefore I must use the survey commands.
> > 
> > In previous versions of stata, I would use the code:
> > 
> > svymean y, by(x)
> > svytest [x]0=[x]1
> > 
> > Stata 8 says that svytest no longer exists and that I should use 
> the lincom 
> > command.  Maybe the coffee hasn't set in, but I cannot figure 
> out how to do 
> > replicate the above code using the lincom command based on the 
> information 
> > from Stata's help screen.
> > 
> > So my question is two-fold:
> > 1 - How do I test group differences using the svy command in 
> Stata 8 based 
> > on my above example?
> > 2 - Is it possible to estimate a one-way anova to detect group 
> differences 
> > with svy commands in Stata 8 based on my above example?
> 
> Here is an example using the auto data (not that I remove the 
> labels so that
> my example appears closer the one above):
> 
> 	. sysuse auto, clear
> 	. label drop _all
> 	. svyset, srs
> 	. svymean mpg, by(foreign)
> 	. test [mpg]0 = [mpg]1
> 
> When the -by()- option is supplied to -svymean-, the name of the 
> variable that
> we are taking the mean of becomes something like an equation 
> identifier when
> used with -test-.  The values of the categories in the -by()- 
> variable are
> used to identify which mean we are talking about.
> 
> Here is the output from the above example:
> 
> ***** BEGIN:
> . sysuse auto, clear
> (1978 Automobile Data)
>                                                                   
>             
> . label drop _all
>                                                                   
>             
> . svyset, srs
> simple random sample (SRS)
>                                                                   
>             
> . svymean mpg, by(foreign)
>                                                                   
>             
> Survey mean estimation
>                                                                   
>             
> pweight:  <none>                                  Number of obs    
> =        74
> Strata:   <one>                                   Number of strata 
> =         1
> PSU:      <observations>                          Number of PSUs   
> =        74
>                                                  Population size  
> =        74
>                                                                   
>             
> -------------------------------------------------------------------
> -----------
> Mean   Subpop. |   Estimate    Std. Err.   [95% Conf. Interval]    
>    Deff
> ---------------+---------------------------------------------------
> -----------
> mpg            |
>    foreign==0 |   19.82692    .6558681    18.51978    21.13407    
>       1
>    foreign==1 |   24.77273    1.386503    22.00943    27.53602    
>       1
> -------------------------------------------------------------------
> -----------
>                                                                   
>             
> . test [mpg]0 = [mpg]1
>                                                                   
>             
> Adjusted Wald test
>                                                                   
>             
> ( 1)  [mpg]0 - [mpg]1 = 0
>                                                                   
>             
>       F(  1,    73) =   10.40
>            Prob > F =    0.0019
> ***** END:
> 
> --Jeff
> jpitblado@stata.com
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