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Re: st: Typo in the .dta description

From   [email protected] (Jeff Pitblado, StataCorp LP)
To   [email protected]
Subject   Re: st: Typo in the .dta description
Date   Wed, 09 Jan 2008 14:33:44 -0600

Sergiy Radyakin <[email protected]> posted a question about the internal
structure of Stata's dta-files.  In it Sergiy asked which data characteristics
to set so that Stata's -svy- commands will recognize that the data was
-svyset- using only a sampling weight variable:

> Another question is regarding the weighting scheme saved in the
> .dta-files. Although weighting is not a part of the file-format
> specification and the scheme is saved by an .ado file for svy commands
> in the dataset characteristics, it would be nice to have a
> description, of which exactly dataset characteristics must be set by
> an external program, so that Stata recognizes the weighting
> automatically.

Stata's -svyset- command has gone through a few design updates, and the
current design does not lend itself to Sergiy's simple request.  Fortunately
an earlier design does and the -svy- commands are backward compatible.

The simplest way for an external program to generate a dataset so that it will
be recognized as -svyset- with -pweight-s is to specify the following data

	characteristic		value
	_dta[_svy]		"set"
	_dta[pweight]		variable name containing the sampling weights

Note that abbreviating the name of the weight variable will cause problems for
Stata users that set variable abbreviation off (see -help set varabbrev-).

Here is a simple example in Stata that sets the characteristics directly
instead of using the -svyset- command.

***** BEGIN:
. sysuse auto
(1978 Automobile Data)

. svyset
no survey characteristics are set

. char _dta[_svy] "set"

. char _dta[pweight] "displacement"

. svyset

      pweight: displacement
          VCE: linearized
  Single unit: missing
     Strata 1: <one>
         SU 1: <observations>
        FPC 1: <zero>

. svy: mean mpg turn
(running mean on estimation sample)

Survey: Mean estimation

Number of strata =       1          Number of obs    =      74
Number of PSUs   =      74          Population size  =   14600
                                    Design df        =      73

             |             Linearized
             |       Mean   Std. Err.     [95% Conf. Interval]
         mpg |   19.42267   .6027065      18.22148    20.62386
        turn |   41.21781   .5582319      40.10525    42.33036
***** END:

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