"Robert Bozick" <[email protected]> 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
[email protected]
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