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st: Re: statalist-digest V4 #1693


From   "Carlos Elordi" <celordi@wirthlin.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Re: statalist-digest V4 #1693
Date   Fri, 6 Aug 2004 12:52:31 -0400

Dear statalist members,
In attempting to replicate the latent class model for rankings from the
Gllamm manual, I keep running into trouble when issuing the last portion of
the command (see below). I get that initial values are not feasible, and the
r(1400) Stata error message (numerical overflow). Using weights, the
effective observations are about 20,000.
For a reference to this model see section 9.4 in Gllamm manual (October 28,
2001).
I use the latest version of both Stata (8.2 Special Edition) and Gllamm.

Below is the output from the latent class example with rankings, when
running Gllamm (this is the last step, after reshaping the data).

I would appreciate any comment on this.

Best regards,
Carlos


. gllamm item alt1 alt2 alt3, expand(set chosen o) i(patt) link(mlogit) /*
> */ family(binom) nrf(3) eqs(alt1 alt2 alt3) nocons weight(wt) nip(2) /*
> */ ip(f) trace

General model information
----------------------------------------------------------------------------
--

dependent variable:         item
nominal responses:          mlogit
denominator:                1
equation for fixed effects  alt1 alt2 alt3

Random effects information for 2 level model
----------------------------------------------------------------------------
--



***level 2 (patt) equation(s):
   (3 random effect(s))


class 1

   location for random effect 1
   z2_1_1: alt1

   location for random effect 2
   z2_2_1: alt2

   location for random effect 3
   z2_3_1: alt3

   log odds for level 2
   p2_1: _cons

number of level 1 units = 20358
number of level 2 units = 2262

Initial values for fixed effects

(using gllamm for inital values)

----------------------------------------------------------------------------
--
Iteration 0:
Coefficient vector:
     item:  item:  item:
     alt1   alt2   alt3
r1      0      0      0

initial values not feasible
(error occurred in ML computation)
(use trace option and check correctness of initial model)
r(1400);

end of do-file
r(1400);


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