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Re: st: sd(constant) with xtmixed

From   Maarten Buis <>
Subject   Re: st: sd(constant) with xtmixed
Date   Fri, 8 Feb 2013 12:14:00 +0100

On Fri, Feb 8, 2013 at 11:55 AM, Carmen Blanco wrote:
> In my multilevel estimation Stata reports me sd(constant)  at the
> level 95% of significance. Could someone tell me, please, how to
> calculate sd(constant) at the level 99% of significance in xtmixed
> estimation.

In a multilevel random effects model you assume that the constant
differs across higher level units (persons if you have multiple
measurement on the same persons, classrooms if you have students
nested in classrooms, herds if you have cows nested in herds, etc.).
You do not measure the different constants but assume that they follow
a normal distribution, and you estimate the standard deviation of that
distribution. That is what sd(constant) is. So there is no level of
significance associated with that estimate, the point estimate is just
what it is and it won't change if you change the level of

There is a level of significance associated with the confidence
interval around sd(constant). You can change that by adding the
-level(99)- option to your estimation command.

Hope this helps,

Maarten L. Buis
Reichpietschufer 50
10785 Berlin
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