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From |
Stas Kolenikov <skolenik@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: interaction in SEM |

Date |
Wed, 7 Dec 2011 11:13:14 -0600 |

On Wed, Dec 7, 2011 at 10:01 AM, Zhi Su <su.zh@husky.neu.edu> wrote: > Thanks for the suggestion. Here t is an observed dummy variable. > I have also looked into -gllamm-, but found it is hard to understand > the manual. So I turn to -sem-. Since -sem- does not support nonlinear > latent varaible, is there any examples for using -gllamm- to estimate > model as mine? It is better the example has the codes, results and > explanation for the codes and recults. You'd have to look at the manual. With some exceptional luck, you might find an example on gllamm.org website, but your model is a rather non-standard one, so you may or may not be able to find anything convincing. With -gllamm-, you would need to -reshape long- your data into one outcome (or indicator) per line, nested in your original observations, and create the variables that would provide the match between your latent, and your outcomes and indicators. For the indicators -a1- and -a2-, you will have dummy variables identifying the (reshaped long) observations that came from these indicators. Their coefficients will be the loadings in the measurement model. For the outcome -Y-, you'd have to have a dummy that identifies this variable for -gllamm-, and its interactions with -t- and -x-. You would also need to put its interaction with -t- into the equation for the latent variable, so all in all you will have something like eq AA : dummy_for_a1 dummy_for_a2 dummy_for_y_times_t gllamm dummy_for_a1 dummy_for_a2 dummy_for_y dummy_for_y_times_t dummy_for_y_times_x , id( original_observation) eq( AA ) > And why do you think my model can not be identified? Just a gut feeling. If you had three or more indicators of A, I would not have issues. The factor models with two indicators per factor are only identified if there are more than one factor with correlations between them, however, you only have one latent variable. If the model is not identified, a way to force identification is to impose constraint, e.g., the loadings of -a1- and -a2- are the same, or the loadings sum up to 1, etc. -- Stas Kolenikov, also found at http://stas.kolenikov.name Small print: I use this email account for mailing lists only. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**Re: st: interaction in SEM***From:*Zhi Su <su.zh@husky.neu.edu>

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