Re: st: SVY medians and Elixhauser

[Mike Butterfield <mcbutterfield@gmail.com>]

Hi Steve (thanks for the reference) and Stas- I had some trouble with
epctile and wanted to get your opinion on whether this is ‘legal’
(legitimate) to do.


1.  I tried to get median ages for my patients with portal vein
thrombosis (pvt) for both those with& without cirrhosis, but I had
some strata with single observations.

2.  I identified the strata and excluded them (~6 observations), and
got it to work.

3.  Is ok to do? Output for non cirrhotics is below.

a.  This didn’t work:

 . epctile AGE, p(50) over(cirr) svy speclab subpop(pvt if AGE>=18 & AGE<=90)

(running mean on estimation sample)

Survey: Mean estimation

Number of strata =      53          Number of obs    =    3665

Number of PSUs   =     482          Population size  =   18356

                                    Subpop. no. obs  =    3665

                                    Subpop. size     =   18356

                                    Design df        =     429



            0: cirr = 0

            1: cirr = 1



--------------------------------------------------------------

             |             Linearized

        Over |       Mean   Std. Err.     [95% Conf. Interval]

-------------+------------------------------------------------

__000006     |

           0 |  -.0236348          .             .           .

           1 |  -.0477322          .             .           .

--------------------------------------------------------------

Note: missing standard errors because of stratum with single

      sampling unit.

estimates post: matrix has missing values

r(504);





b. this did:



svydes AGE if AGE>=18 & AGE<90 & pvt==1 & cirr==0



Survey: Describing stage 1 sampling units



      pweight: DISCWT

          VCE: linearized

  Single unit: missing

     Strata 1: NIS_STRATUM

         SU 1: HOSPID

        FPC 1: <zero>



                             #Obs with  #Obs with     #Obs per included Unit

           #Units    #Units   complete  missing   ----------------------------

Stratum   included  omitted     data      data      min       mean      max

--------  --------  --------  --------  --------  --------  --------  --------

    2111         1*        0         1         0         1       1.0         1

    2412         1*        0         1         0         1       1.0         1

    3111         1*        0         1         0         1       1.0         1

    3112         1*        0         1         0         1       1.0         1

    3121         1*        0         1         0         1       1.0         1

    4112         1*        0         1         0         1       1.0         1

    4122         1*        0         4         0         4       4.0         4

--------  --------  --------  --------  --------  --------  --------  --------

      51       399         0      1495         0         1       3.7        69

                              ------------------

.  epctile AGE, p(50) svy speclab subpop(pvt if AGE>=18 & AGE<=90 &
cirr==0 & NIS_STRATUM ~=2111 & NIS_STRATUM ~=2412 & NIS_STRATUM ~=3111
& NIS_STRATUM ~=3112 & NIS_STRATUM ~=3121 & NIS_STRATUM ~=4112)



Number of strata =      44          Number of obs    =    1492

Number of PSUs   =     394          Population size  =  7486.8

                                    Subpop. no. obs  =    1492

                                    Subpop. size     =  7486.8

                                    Design df        =     350


...


Percentile estimation

------------------------------------------------------------------------------

             |             Linearized

         AGE |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]

-------------+----------------------------------------------------------------

         p50 |         56        .75    74.67   0.000     54.53003    57.46997



Mike

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