Dear statalist users,
I need to compare means in a cluster study. I use the svymeans and lincom commands and I get the following output. My question is: why the CIs for the means overlap so much but the p-value is significant?
Thanks a lot!
Montse Rue
Lleida (Spain)
svyset,psu( oftal)
psu is oftal
. svymean vftotala,by(fase)
Survey mean estimation
pweight: <none> Number of obs = 837
Strata: <one> Number of strata = 1
PSU: oftal Number of PSUs = 19
Population size = 837
------------------------------------------------------------------------------
Mean Subpop. | Estimate Std. Err. [95% Conf. Interval] Deff
---------------+--------------------------------------------------------------
vftotala |
fase==0 | 62.94243 3.114908 56.39826 69.48661 10.60526
fase==1 | 66.69508 2.276287 61.91277 71.47738 7.967125
------------------------------------------------------------------------------
. lincom [vftotala]0-[vftotala]1
( 1) [vftotala]0 - [vftotala]1 = 0
------------------------------------------------------------------------------
Mean | Estimate Std. Err. t P>|t| [95% Conf. Interval]
-------------+----------------------------------------------------------------
(1) | -3.752642 1.615128 -2.32 0.032 -7.145901 -.3593839
------------------------------------------------------------------------------
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