An $N_m$ x 3 data matrix for MZ twins. $N_m$ is the number of MZ twin pairs. The first two columns are centered trait values (i.e. the mean should be zero) and the third column is age (or other covariates).
data_d
An $N_d$ x 3 data matrix for DZ twins. $N_d$ is the number of DZ twin pairs. The first two columns are centered trait values (i.e. the mean should be zero) and the third column is age (or other covariates).
knot_a
The number of interior knots for the A component. The default value is 8.
knot_c
The number of interior knots for the C component. The default value is 8.
eps
Tolerance for convergence of the EM algorithm iterations. The default value is 0.1.
Value
varThe estimated variance of the E component.
var_b_aThe estimated variance for the penalized coefficient for the A components.
var_b_cThe estimated variance for the penalized coefficient for the C components.
beta_cThe estimated spline coefficients of the A component.
beta_aThe estimated spline coefficients of the C component.
conAn indicator of convergence of the optimization algorithm. An integer code 0 indicates successful completion. See 'optim' for more details.
likThe minus log marginal likelihood.
knot_aThe values of the knots for the A component.
knot_cThe values of the knots for the C component.
References
He, L., Sillanp��, M. J., Silventoinen, K., Kaprio, J., & Pitk�niemi, J. (2016). Estimating Modifying Effect of Age on Genetic and Environmental Variance Components in Twin Models. Genetics, genetics-115.