S E Håberg, S J London, H Stigum, et al. Folic acid supplements in pregnancy and early childhood respiratory health. Arch Dis Child 2009;94:180–4. In table 2 of this paper the column labelled “n” refers to number of children within each exposure group for folic acid supplements in pregnancy, and not to number of children with wheeze. The heading “wheeze, 6–18 months” applies only to the % and aRRs (95% CI).