[1] Aarhus Univ, Danish Epidemiol Sci Ctr, DK-8000 Aarhus C, Denmark
[2] Univ Alabama, Dept Maternal & Child Hlth, Birmingham, W Midlands, England
[3] Univ Copenhagen, Dept Social Med, DK-1168 Copenhagen, Denmark
[4] Univ Copenhagen, Dept Biostat, DK-1168 Copenhagen, Denmark
[5] Harvard Univ, Dept Organism & Evolutionary Biol, Boston, MA 02115 USA
[6] Aarhus Univ, Dept Pediat, DK-8000 Aarhus C, Denmark
[7] Univ Calif Davis, Dept Epidemiol & Prevent Med, Davis, CA 95616 USA
[8] Univ Bergen, Sect Med Stat, N-5020 Bergen, Norway
[9] Natl Inst Environm, Epidemiol Branch, Durham, NC USA