Affiliation: | (1) Medical Statistics Unit, University of Edinburgh, Teviot Place, EH8 9AG Edinburgh;(2) Department of Geology, University of Edinburgh, West Mains Road, EH9 3JW Edinburgh;(3) Department of Community Medicine, University of Edinburgh, Teviot Place, EH8 9AG Edinburgh;(4) Present address: London Scientific Services, County Hall, SE1 7PB London |