7 Department of Statistics, University of Oxford, Oxford, OX1 3TG, UK.
8 UCL Genetics Institute, University College London, London, WC1E 6BT, UK.
9 Wellcome Trust Centre for Human Genetics, OX3 7BN, Oxford, UK. Jflint@mednet.ucla.edu.
10 Center for Neurobehavioral Genetics, Semel Institute for Neuroscience and Human Behavior, University of California, LosAngeles, Los Angeles, California, 90095-1761, USA. Jflint@mednet.ucla.edu.