! Sibling Interaction Model
! CBC data in US twins

G1: genetic structure
Data Calc NGroups=3
Begin Matrices;
X Lower 1 1 Free  ! genetic structure
Z Lower 1 1 Free  ! specific environmental structure
B Symm 2 2        ! sibling interaction parameters
I Iden 2 2
End Matrices;
Specify B 0 3 0
Begin Algebra;
A= X*X' ;
E= Z*Z' ;
P= (I-B)~;
End Algebra;
End

G2: Male MZ twins in larger families
Data NInput_vars=2 NObservations=171
Labels exter1 exter2
CMatrix Symmetric File=uscbcmz.cov
Matrices= Group 1
Covariances P* (A+E | A _
                A   | A+E) * P' /
Options RSidual
End 

G4: Male DZ twins in larger families
Data NInput_vars=2 NObservations=194
Labels exter1 exter2
CMatrix Symmetric File=uscbcdz.cov
Matrices= Group 1
H Full 1 1
Covariances P* (A+E | H@A _
                H@A | A+E) * P' /
Matrix H .5
Start .3 All
Start .0 B 1 2 1 
Options NDecimals=4
Options RSidual
End