Figure 2.

The selection of the population included in this study. First, participants were excluded based on age. Participants younger than 4 years of age or older than 50 years of age were excluded. Second, data spanning three generations was required to investigate a possible association between grandmaternal smoking during pregnancy and asthma in grandchildren. Therefore, participants who could not provide data on both childhood asthma and grandmaternal smoking were excluded. We investigated maternal grandmaternal smoking as well as paternal grandmaternal smoking and therefore those reporting on either one or both were included.