Meaning of "variance" in LTM when out... PreviousNext Mplus
Discussion > Growth Modeling of Longitudinal Data >  Kristie
Long posted on Tuesday, January 11, 2000 - 12:43 pm In order to
estimate a growth model with categorical data, a
parameterization requirement of the mean intercept must be fixed
to zero.  Can you explain the rationale for the fixed mean and
the interpretation of the intercept variance?  Bengt O.
Muthen posted on Tuesday, January 11, 2000 - 4:26 pm The
intercept should be fixed at zero because the means of the
categorical outcomes are modeled by the threshold parameters, so
we don't need both types of parameters. By intercept variance I
assume you mean the intercept factor variance. The variance
should be understood in the metric of the probit regression of
each outcome on the growth factors. Variances can then be seen
as contributing to the y* variance as discussed in Appendix 1 of
the User's Guide. Here, the residual variance is fixed at 1.
Ultimately, I think one has to judge the intercep