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Stata FAQ
How can I do a t-test with survey data?

There is no svy: ttest command in Stata, however svy: mean is a "true" estimation command and allows for the use of both the test and lincom post-estimation commands. It is also easy to do a t-test using the svy: regress command.

We will illustrate this using the hsb2 dataset pretending that the variable socst is the sampling weight (pweight) and that the sample is stratified on ses. Let's say that we wish to do a t-test for write by male/female. 

use http://www.ats.ucla.edu/stat/stata/notes/hsb2, clear

svyset [pw=socst], strata(ses)

      pweight: socst
          VCE: linearized
     Strata 1: ses
         SU 1: 
        FPC 1: 

svy: mean write, over(female)
(running mean on estimation sample)

Survey: Mean estimation

Number of strata =       3          Number of obs    =     200
Number of PSUs   =     200          Population size  =   10481
                                    Design df        =     197

         male: female = male
       female: female = female

--------------------------------------------------------------
             |             Linearized
        Over |       Mean   Std. Err.     [95% Conf. Interval]
-------------+------------------------------------------------
write        |
        male |   51.65351   1.041066      49.60045    53.70658
      female |   55.81467    .721354       54.3921    57.23723
--------------------------------------------------------------

test [write]male = [write]female

Adjusted Wald test

 ( 1)  [write]male - [write]female = 0

       F(  1,   197) =   10.45
            Prob > F =    0.0014

lincom [write]male - [write]female

 ( 1)  [write]male - [write]female = 0

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      t    P>|t|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
         (1) |  -4.161156     1.2871    -3.23   0.001    -6.699419   -1.622892
------------------------------------------------------------------------------

svy: regress write female

(running regress on estimation sample)

Survey: Linear regression

Number of strata   =         3                  Number of obs      =       200
Number of PSUs     =       200                  Population size    =     10481
                                                Design df          =       197
                                                F(   1,    197)    =     10.45
                                                Prob > F           =    0.0014
                                                R-squared          =    0.0519

------------------------------------------------------------------------------
             |             Linearized
       write |      Coef.   Std. Err.      t    P>|t|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
      female |   4.161156     1.2871     3.23   0.001     1.622892    6.699419
       _cons |   51.65351   1.041066    49.62   0.000     49.60045    53.70658
------------------------------------------------------------------------------

test female

Adjusted Wald test

 ( 1)  female = 0

       F(  1,   197) =   10.45
            Prob > F =    0.0014
Regardless of the method that we use, we obtain an F-ratio of 10.45 and a t-value of 3.23 with a p-value of 0.0014.

Note: This FAQ was inspired by several responses to a question on the Statalist.

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