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# st: Confidence intervals for survey data from the estimation matrices

 From "Darren White" To Subject st: Confidence intervals for survey data from the estimation matrices Date Wed, 20 Jul 2011 12:55:18 +1000

```Hello,

I am attempting to compile estimate tables directly from STATA's temporary estimate matrices, however none of the listed matrices after command: ereturn list (below) contain the confidence intervals that are displayed using the svy: command in STATA (table below). Also the estimate variance matrix e(V) and the square root e(V) x 1.96 +/- give the estimates in the automatic estimate display ( below at bottom) after some renaming of the e(b) and e(V) matrices but these are different to those returned form the svy: tab command.

Can anyone tell me how STATA arrives at the confidence interval estimates using the svy: tab command and where they could be found in the matrix environment? Alternatively how would I replicate the calculation routine for survey data using the variance provided in the e(V) matrix? The e(b) matrix has the same percentage estimates as returned form the svy: tab agecat bmicat, ci command

Any help or suggestions would be greatly appreciated

Darren White
Population Epidemiology Unit
Queensland Health
Brisbane
Australia

___________________________________________________________________
. svy: tab  agecat bmicat, ci per
(running tabulate on estimation sample)

Number of strata   =         1                  Number of obs      =         7
Number of PSUs     =         7                  Population size    =         7
Design df          =         6

-------------------------------------------------
bmicat | percentages           lb           ub
----------+--------------------------------------
1 |       42.86               9.06        84.95
2 |       57.14             15.05        90.94
|
Total |         100
-------------------------------------------------
_____________________________________________________________________
. ereturn list

scalars:
e(stages) =  1
e(census) =  0
e(singleton) =  0
e(N_strata_omit) =  0
e(df_r) =  6
e(N) =  7
e(N_strata) =  1
e(N_psu) =  7
e(N_pop) =  7
e(r) =  1
e(c) =  2
e(total) =  7
e(mgdeff) =  .
e(cvgdeff) =  .
e(rank) =  1

macros:
e(cmdline) : "svy : tab  agecat bmicat, ci per"
e(cmd) : "tabulate"
e(prefix) : "svy"
e(cmdname) : "tabulate"
e(marginsnotok) : "_ALL"
e(predict) : "_no_predict"
e(estat_cmd) : "svy_estat"
e(colvar) : "bmicat"
e(rowvar) : "agecat"
e(setype) : "cell"
e(vcetype) : "Linearized"
e(vce) : "linearized"
e(wtype) : "pweight"
e(wvar) : "weight"
e(wexp) : "= weight"
e(singleunit) : "missing"
e(depvar) : "Mean"
e(properties) : "b V"

matrices:
e(b) :  1 x 2
e(V) :  2 x 2
e(V_srs_col) :  2 x 2
e(Deft_col) :  1 x 2
e(Deff_col) :  1 x 2
e(V_srs_row) :  1 x 1
e(Deft_row) :  1 x 1
e(Deff_row) :  1 x 1
e(V_srs) :  2 x 2
e(Deft) :  1 x 2
e(Deff) :  1 x 2
e(V_col) :  2 x 2
e(V_row) :  1 x 1
e(Col) :  1 x 2
e(Row) :  1 x 1
e(Prop) :  1 x 2
e(Obs) :  1 x 2
e(_N_strata_certain) :  1 x 1
e(_N_strata_single) :  1 x 1
e(_N_strata) :  1 x 1
_________________________________________________________________________________________
.	ereturn post b V

.	ereturn display

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

p11    .4285714	.2020305	2.12	0.034	.0325989	.8245439
p12    .5714286	.2020305	2.83	0.005	.1754561	.9674011

________________________________________________________________________________________

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