Re: st: "Select If" Statement xtmixed

[Maarten buis <maartenbuis@yahoo.co.uk>]

--- On Thu, 17/3/11, Saul G. Alamilla wrote:
> I would like to use a "select if" statement in xtmixed
> so that I only utilize clusters (L2 units or groups)
> containing at least 3 observations (or L1 units). 

I am assuming you want not just a minimum of two 
observations, but a minimum of two _valid_ observations.

say you have a dependent variable (y) and two independent
variables (x1 and x2). Than the first step would be to 
create a variable that says whether or not an observation
has all valid values:

gen byte valid = !missing(y, x1, x2)

Than you create a variable that says whether or not a 
cluster contains >2 valid observations:

bys group valid : gen byte touse = _N > 2 if valid == 1

To create these variables I used tricks discussed her:
<http://www.stata.com/support/faqs/data/trueorfalse.html>

after that you use that variable in the if condition (not 
option!) in -xtmixed-:

xtmixed y x1 x2 if touse == 1 || group_id:

-if- conditions (and weights) are placed immediately 
after the variable list, options are placed after the
comma.

Hope this helps,
Maarten

--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany

http://www.maartenbuis.nl
--------------------------


      

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