For each disorder we assume the random effects are independent between families, but dependent within families with the correlations given in Table 1. The model includes cross-disease covariances: σszbpa is the additive-genetic covariance of schizophrenia and bipolar effect, and similarly σszbpf and σszbpc are the adult and childhood environmental effects. All parameters were estimated simultaneously using the maximum likelihood method25, where the likelihood is computed using a fast Monte Carlo integration of the random effects26.
