Hi,
I am quietly new to Openmx and thankful for any help that I can get.
I have repeated measurement of continuous variable over two time periods to which I would to do similar analysis as in the De Geus et al (2007) : Bivariate Genetic Modeling of Cardiovascular Stress Reactivity: Does Stress Uncover Genetic Variance?.
I am starting from the script (http://www.vipbg.vcu.edu/vipbg/HGEN619/BivTwinMaRawCon.R) of bivariate cholesky by Hermine Maes. What I would to do is to add a test of genetic amplification (a11=a21?) as well as whether there is a new gene that comes into play later stage in life (a22=0?).
Thankful for any help to formulate this new addition to the model!
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I think you have the right idea. One other possibility is that you may be interested in whether overall genetic variance increases (regardless of whether it comes from new genetic factors or the same ones with greater force). This could be tested by implementing a non-linear constraint such that A[1,1] == A[2,2] where A is the matrix that results from the product of the lower Cholesky matrices, i.e., A = a %*% t(a).