1 Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden; Astrid Lindgren Children's Hospital, Lung and Allergy Unit, Karolinska University Hospital, Stockholm, Sweden. Electronic address: catarina.almqvist@ki.se.
2 Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
3 Department of Psychological and Brain Sciences, Indiana University, Bloomington, Ind.