For age at menarche, the ALSPAC sample made up 7% of the GWAS discovery sample.
All other scores were weighted according to the association magnitude of each single nucleotide polymorphism (SNP) in the original GWAS.
Of these initial pregnancies, there were a total of 14 676 fetuses, resulting in 14 062 live births and 13 988 children who were alive at 1 year of age.
The children and their mothers have been followed up through postal questionnaires and at clinics.
We included only children who had been enrolled in the study during the first phase of data collection and survived to age 1 year (resulting in the exclusion of five children and 43 mothers from the analysis sample).
Please note that the study website contains details of all the data that are available through a fully searchable data dictionary: [
The ALSPAC cohort was not included in the GWAS that generated the summary statistics for these traits, except for education and age at menarche.
For education, we used summary statistics excluding ALSPAC and 23andme, which were obtained directly from the study authors.
It is often assumed that selection (including participation and dropout) does not represent an important source of bias in genetic studies.
However, there is little evidence to date on the effect of genetic factors on participation.