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3 Fitting a Phenotypic Factor Model
Martin et al. (1985) obtained data on
arithmetic computation from male and female twins who were measured
once before and three times after drinking a standard dose of
alcohol. To illustrate the use of a confirmatory
factor analysis model in Mx, we analyze data from MZ females
(first born twin only). The observed variances and correlations are
shown in Table 10.1. The confirmatory model is one in which a
single latent factor is hypothesized to account for all the
covariances among the four variables. The Mx script below shows
the model specifications and the input matrix.
Table 10.1:
Observed correlations (with
variances on the diagonal) for arithmetic computation variables from
female MZ twins before (time 0) and after (times 1  3) standard
doses of alcohol.






Time 0 
Time 1 
Time 2 
Time 3 
Time 0 
259.66 



Time 1 
.81 
259.94 


Time 2 
.83 
.87 
245.24 

Time 3 
.87 
.87 
.90 
249.30 
Next: Mx Script for Phenotypic
Up: 2 Phenotypic Factor Analysis
Previous: 2 Building a Phenotypic
Index
Jeff Lessem
20020321