Creating a 2000 IES-LFS Database in Stata



PROVIDE Project Technical Paper 2005:1

February 2005


PSU:      <observations>

Number of PSUs

26177

Population size =  11221840

-----------

Mean |

Estimate

Std. Err.

[95% Conf.

Interval]

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

Deff

totinc |
_ _ _ _ _ _ _ _ _ _ _ _

42793.12

725.4612

41371.18

44215.06

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

1.232494

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

The ci command with the aweight option gives the exact same point estimates as svymean
with pweight. However, the standard errors are different since aweight uses a different
formula for the standard error. The standard error of the point estimate, which should not be
confused with the standard deviation of a variable, as well as the 95% confidence interval of
the estimate, is slightly larger when
pweight is used.

As argued before it is also important to specify clustering and stratification if applicable.
The IES 2000 data used in this example made use of clusters (PSUs) and stratification along
provincial and rural/urban lines (variable
provloc). In the two examples that follow svyset psu
psuno
is specified, and thereafter svyset strata provloc is added.12 In each instance the point
estimates are shown. Notice the effect on the standard error, confidence interval and
deff (see
section 2.2.3).

. svyset psu psuno

. svymean totinc

Survey mean estimation

pweight: wgtselect

Strata:   <one>

PSU:      psuno

Number of obs    =     26177

Number of strata =         1

Number of PSUs   =      2956

Population size  =  11221840

-----------

Mean |

Estimate

Std. Err.

[95% Conf.

Interval]

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

Deff

totinc |
_ _ _ _ _ _ _ _ _ _ _ _

42793.12

1042.246

40749.52

44836.72

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

2.543879

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

. svyset strata provloc

. svymean totinc

Survey mean estimation

pweight: wgtselect

Strata:   provloc

PSU:      psuno

Number of obs    =     26177

Number of strata =        18

Number of PSUs   =      3327

Population size  =  11221840

-----------

Mean |

Estimate

Std. Err.

[95% Conf.

Interval]

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

Deff

totinc |
_ _ _ _ _ _ _ _ _ _ _ _

42793.12

975.1044

40881.25

44704.99

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

2.226684

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

12 Variable psuno is supplied by Statistics South Africa. Variable provloc, which represents the strata in the
survey, was created by grouping variables for province (
prov) and location.

9

© PROVIDE Project



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