[1] UK Cochrane Ctr, Oxford OX2 7LG, England
[2] Trinity Coll Dublin, Sch Nursing & Midwifery, Dublin, Ireland
[3] Childrens Hosp Eastern Ontario, Res Inst, Chalmers Res Grp, Ottawa, ON K1H 8L1, Canada
[4] Univ Ottawa, Fac Med, Dept Epidemiol & Community Med, Ottawa, ON, Canada
[5] Univ Adelaide, Discipline Obstet & Gynaecol, Adelaide, SA, Australia
[6] Univ Oxford Wolfson Coll, Ctr Stat Med, Oxford OX2 6UD, England
[7] Family Hlth Int, Durham, NC USA