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Re: st: confirmatory factor analysis using gllam in stata


From   Stas Kolenikov <skolenik@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: confirmatory factor analysis using gllam in stata
Date   Mon, 17 Jan 2011 10:49:11 -0600

Have you tried -confa- command that I presented in SJ 9(3)? I think I
also show the relation between -confa- and -gllamm- somewhere in
supplementary do-files. The -eq- command here tells -gllamm- that the
first factor loads on the first five observations within the -i(id)-
group, the second factor, on the next five observations, and the third
one, on the remaining ones. The loadings are constrained to be the
same though, which may or may not be what you want.

On Sun, Jan 16, 2011 at 9:10 PM, Hong, Sounman
<sounman_hong@hksphd.harvard.edu> wrote:
> My question build upon a previous Q&A. I found a question that is fundamentally the same as mine. But I cannot understand the posted answer.
>
> Let's first look at the question and answer.
>
> This is the question.
>
>> Hi all,
>
>> I have a scale composed of 15 variables (items in a 5-point likert scale) that correspond to 3 factors/domains. How do I run CFA using gllamm.
>
>> My data:
>
>> Suppose the variable names are x1-x15 and the factors are f1 f2 and f3.
>
>> f1 corresponds to variables x1-x5
>> f2 corresponds to variables x6-x10
>> f2 corresponds to variables x11-x15
>
>> I tried using the eq syntax to define the factors (equations) using the following syntax:
>
>> eq f1: x1-x5
>> eq f2: x6-x10
>> eq f3: x11-x15
>
>> but where do I go from here? I'll not even post all my attempts.
>
>> Any ideas?
> ===============================
> This is the answer posted for the question
> If that's a linear model, then first you need to -reshape-
> your data so that each variable is now an observation within a block
> corresponding to one unit:
>
> g long ID = _n
> reshape long x, i(ID)
>
> Then you need to link your factors to your variables (which are now
> observations):
>
> bysort ID: g byte d1 = _n<6
> by ID: g byte d2 = (_n>5) & (_n<11)
> by ID: g byte d3 = _n > 10
> g byte ones = 1
>
> Now define your equations:
>
> eq 101 : ones d1 d2 d3
> eq 102 : ones d1 d2 d3
> eq 103 : ones d1 d2 d3
>
> Now you are ready to run -gllamm-:
> gllamm x, i(id) eqs(101 102 103) nrf(3)
> =============================
> So, my question is that I don't understand the "eq" commands in the answer above.
> It seems like the answer defines three equations with 3 factor variables and the variable "ones". But why?
> I was thinking the following.
>
> eq factor1 : d1
> eq factor2 : d2
> eq factor 3: d3
> gllamm x, i(id) eqs(d1 d2 d3) nrf(3)
>
> Is there anything wrong with my stata codes??
> What is the difference between my command and the answer posted above?
> How should I change it?
> Any idea? Any reply would be greatly appreciated.
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
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> *   http://www.ats.ucla.edu/stat/stata/
>



-- 
Stas Kolenikov, also found at http://stas.kolenikov.name
Small print: I use this email account for mailing lists only.

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