1 Christchurch Health and Development Study, Department of Psychological Medicine, University of Otago, Christchurch, New Zealand; Department of Psychology, Speech & Hearing, University of Canterbury, Christchurch, New Zealand.
2 Christchurch Health and Development Study, Department of Psychological Medicine, University of Otago, Christchurch, New Zealand.
3 Social & Behavioural Research Unit, Department of Preventive & Social Medicine, University of Otago School of Medicine, Dunedin, New Zealand.