Different age (covariate) for siblings

Dear all,
I’m working on the bivariate ACE model from 2016 Boulder workshop from Hermione Maes ‘twoSATja’ and ‘twoACEja’ (http://ibg.colorado.edu/cdrom2016/maes/UnivariateAnalysis/scriptsOpenMx.shtml). I use questionnaire data and some participants filled this out one or two years later than their twin siblings, this means that some siblings differ in age. How do I adjust the model to allow different ages between twins? I keep running into problems with non-conforming arrays…

Below the parts of the script that I have trouble adapting:


# Select Covariates for Analysis
ordData[,'age'] <- ordData[,'age']/100
ordData <- ordData[-which(is.na(ordData$age)),]
covVars <- c('age')
nc <- 2 # number of covariates


I adapted the above code to:


twindata$age1<-twindata$age1/100
twindata$age2<-twindata$age2/100
covVars <-c('age1', 'age2')
nc <-2


But I keep having trouble adapting the defAge, pathB and expMean in code below:


# PREPARE MODEL

# ACE Model
# Create Matrices for Covariates and linear Regression Coefficients
defAge <- mxMatrix( type="Full", nrow=1, ncol=1, free=FALSE, labels=c("data.age"), name="Age" )
pathB <- mxMatrix( type="Full", nrow=nc, ncol=1, free=TRUE, values=.01, label=labBe, name="b" )

# Create Algebra for expected Mean Matrices
meanG <- mxMatrix( type="Full", nrow=1, ncol=ntv, free=frMV, values=svMe, labels=labMe, name="meanG" )
expMean <- mxAlgebra( expression= meanG + cbind(t(b%*%Age),t(b%*%Age)), name="expMean" )
thinG <- mxMatrix( type="Full", nrow=nth, ncol=ntvo, free=TRUE, values=svTh, lbound=lbTh, labels=labTh, name="thinG" )
inc <- mxMatrix( type="Lower", nrow=nth, ncol=nth, free=FALSE, values=1, name="inc" )
threG <- mxAlgebra( expression= inc %*% thinG, name="threG"

Thanks for you help!