Re: st: svrest & svresttest commands

[Nick Winter <nw53@cornell.edu>]

At 03:47 PM 6/14/2004 -0700, you wrote:
> Hi everyone,
> I am using the svrmean command to calculate the mean of variable by race and
> gender.  I then want to see if difference in mean between males and females
> among whites is significantly different from the gender difference in other
> races.  I gather that fro this I need to use the svrest and svresttest
> commands.  However, I do not know how to access the mean values after the
> estimation command and do the test.  This is what I am doing (0 and 1 stand
> for males and females respectively):
> . svrest "svrmean usc, by (smallrace pcpreq)"
> "[white]0-[white]1-[latino]0+[latino]1"
> error when command executed on original dataset
> invalid syntax
> r(101);
> Please help.
> Thanks.
> Arpita
Greetings,

As author of these programs, I'll take a crack at this.

I think in this case you don't actually need -svrest-, since you can use 
-svrmean- to get the basic means and their (co)variances.  -svrest- is 
designed to let you do replication-based variance estimation for models and 
commands that don't have prepackaged svr-based programs already; this is 
not the case for means.  (Think heckman, or user-written -nl- programs, etc.)

So in this case you can just use -svrmean-, followed by -test-:

        . svymean usc, by(smallrace pcpreq)
        . test [usc]1-[usc]2-[usc]3+[usc]4=0

(You will need to look at the handy key provided by -svrmean- to get the 
mappings between values of your by() variables and the values 1, 2, 3 and 4 
displayed in the output).

Note also that -test- now recognizes the fact that the previous command was 
a -svy-command, so there is no need for -svytest-; my -svr- commands 
masquerade as -svy- commands in this context, so the adjusted test gets done.

--Nick Winter

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