[1] UNIV LEEDS,LEUKAEMIA RES FUND CTR CLIN EPIDEMIOL,LEEDS LS2 9NG,W YORKSHIRE,ENGLAND
[2] ROYAL ABERDEEN CHILDRENS HOSP,ABERDEEN AB9 2ZG,SCOTLAND
[3] INST CHILD HLTH,BRISTOL BS8 8BJ,AVON,ENGLAND
[4] UNIV LEEDS,PAEDIAT EPIDEMIOL GRP,LEEDS LS2 9LN,W YORKSHIRE,ENGLAND