Selection of cases and controls. We used data
from the Nurses’ Health Study II, a cohort
of 116,430 female nurses from 14 U.S. states
that was established in 1989 and has been followed
over time with biennial questionnaires.
Initially nurses were recruited from 14 U.S.
states, but since that time they have moved
throughout the United States. Thus, children
in the current analyses were born in all 50 U.S.
states. In the 2005 questionnaire, respondents
were asked “Have any of your children been
diagnosed with the following diseases?” with
autism, Asperger’s syndrome, or other ASD
listed as separate responses. In 2007–2008, we