Behavioral Genetics Models
Bivariate Cholesky model with one continuous and ordinal variable
Particularly, I am trying to fit a model with one continuous and one ordinal variable. I have found this script but it is modeling only two ordinal variables:
http://ibg.colorado.edu/cdrom2016/maes/UnivariateAnalysis/twoa/twoACEoa.R
Is there a shortcut to only apply the threshold to one variable?
Thanks in advance.
Interpret >1 and negative results from variance parametrisation of twin model
I am using the new parametrization for a bivariate model, as suggested in "Type I Error Rates and Parameter Bias in Multivariate Behavioral Genetic Models".
The results (see below) include an rA correlation that is higher than one.
Am I doing something wrong or I have to interpret the rA correlation as 1?
The phenotypic correlation is .2. Is it be correct to say that is due to 1, -.96 and .2 for A, D and E respectively?
There are also negative values: there is no way to interpret these results, right?
Should I ever need lower bounds in a twin model?
I am currently starting to familiarize myself with different variations of the ACE-model as well as nuclear twin family designs in OpenMx and although coming from econometrics I dreaded working with SEMs so far I find the ride quite exhilarating.
While trying to reproduce certain results from the literature to broaden my understanding I sometimes encounter a strange behavior where I obtain a parameter estimate which is quite close to what I would expect with the only issue being that it is actually negative.
negative path estimate in UMX cholesky
I conducted a Cholesky model with two variables in two time-points, using the uxACE command, and then conducted a model fitting procedure with the umxModify command. The model was an ADE model.
The results I got (a screenshot is attached) make perfect sense in terms of the overall explained variance by genetics. Meaning, if I compute the variance explained by both A and D for each variable (after squaring each path), I get the same amount of explained genetic variance as in the univariate models for each variable.
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Covariate Effect in Liability Threshold Model
I want to write a script for a GxE-interaction with an ordinal outcome and a continuous moderator and was looking for some scripts that include a covariate effect on an ordinal outcome variable.
In this search I found a [script](https://static1.squarespace.com/static/58b2481a9f7456906a3b9600/t/5d9c0be7b3de004d53e6456b/1570507752071/oneACEoa.pdf) by Hermine Maes where she models the effect of the covariate (age) on the mean of the liability distribution of the outcome variable.
Biometrical model fitting
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Cohort Covariate and ACE Estimates
I've been playing around with various ways to include a cohort covariate in a single-factor model. I've tried four approaches, three of which have pretty consistent results and the fourth, which is fairly different. I've attached the four scripts here, as well as a table of selected output (ACE estimates with CIs, factor loadings, and expected means for observed variables).
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best way to (systematically) fit an ADE model
I am trying to fit a longitudinal Cholesky model (two variables in two time-points) with the umxACE and umxModify commands from the umx package.
Mis-specification and model fit interpretation of univariate ACE
I am new to statistical modelling for genetic analysis and after conducting a round of univariate analysis (prior to a future multivariate one) using the umxACE function I have a few questions I would like to ask for help with.
Test Moderation of Standardized Variance Components
since in the conventional moderated ACE model proposed by Purcell it is only possible to test whether there is a significant moderation of the unstandardized genetic, shared and unshared variance components in a phenotype, I was wondering whether it is also possible to test if there is a significant moderation of the standardized variance components.
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