# Example Mx Script

Univariate ACE Twin Model


! Mx ACE script for twin data

#define nvar 1

Group1: Defines Matrices
Calc NGroups=4

Begin Matrices;
! path co-efficients
X Lower nvar nvar free    ! genetic structure
Y Lower nvar nvar free    ! shared environment
Z Lower nvar nvar free    ! non-shared environment

H Full 1 1

End Matrices;

Matrix H .5

Begin Algebra;
! variance matrices
A= X*X';   ! genetic covariance matrix
C= Y*Y';   ! environmental covariance matrix
E= Z*Z';   ! nonshared environmental
!  covariance matrix
End Algebra;

Start 0   X 1 1 to X nvar nvar
Start 0   Y 1 1 to Y nvar nvar
Start 1.5 Z 1 1 to Z nvar nvar

End

Group2: MZ twin pairs
Data NInput_vars=2 NObservations=1500
CMatrix
2.12
1.67	2.08

Labels trait1 trait2

Matrices= Group 1

Covariances A + C + E  |    A + C  _
A + C    |  A + C + E /

Option RS
End

Group3: DZ twin pairs
Data NInput_vars=2 NObservations=2000
CMatrix
1.98
1.25	2.06

Labels trait1 trait2

Matrices= Group 1

Covariances A + C + E  |   H@A + C  _
H@A + C   |  A + C + E /

Option RS
End

Group4: Standardised solution
Calculation

Matrices = group 1

Begin Algebra;

! phenotypic covariance matrix
P = A + C + E;

! diagonal matrix of phenotypic
!  standard deviations
D = \sqrt(\v2d(\d2v(P)));

! phenotypically standardised
!  genetic covariance matrix
T = D~ * A * D~;

! phenotypically standardised
! shared environmental covariance matrix
U = D~ * C * D~;

! phenotypically standardised
! nonshared environmental covariance matrix
V = D~ * E * D~;

! Genetic correlation matrix
G = \stnd(T);

! Shared environmental correlation matrix
S = \stnd(U);

! Nonshared environmental correlation matrix
N = \stnd(V);

End Algebra;

End