Confidence interval in survey analysis

[Ichinose Yuichi]

Dear all,

I have been analyzing survey data in Stata, and I encounter a problem regarding value of confidence interval.

I am using the national survey data to evaluate satisfaction of medical care that was received in Japan.
I used multi-stage random sampling, and pweight was attached to the data.
By using the weight, I would like to calculate point estimate and confidence interval of patient satisfaction in each prefecture (Japan has 47 prefectures).

Originally, our survey had 5 possible answers for each question.
I categorized these answers to two groups: positive and negative answer.

I tried two different ways to calculate the confidence interval, and these two method gave me completely different values.
I am wondering the reason, and which method should I be using for the analysis.

use data.dta, clear

svyset facid [pw=pweight], strata(pref) fpc(Nst) || patid, strata(group) fpc(Nhi) singleunit(certainty)

gen Q20 = .
replace Q20 = 1 if Answer = 5 | 
Answer = 4 | Answer = 3 
replace Q20 = 0 if 
Answer = 2 | Answer = 1

* Method 1
keep if pref == 1
svy: tab Q20, ci

Output:

Mean	Linearized Std Err.	95% CI Lower	95% CI Upper
.9139879	.0323847	.5025009	1.325475

* Method 2
svy: mean Q20, over(pref)

Output:

Mean	Linearized Std Err.	95% CI Lower	95% CI Upper
.9140944	.0060102	.9021265	.9260624

Could anyone explain why I got the different value depending on using "svy:mean" or "svy:tab"?
Also, why the 95CI of svy:tab had much wider range compared to svy:mean?

Sincerely,
Yuichi Ichinose