Table 1 Differences between the designs of asthma cohort studies. In one study [11] the majority of study participants were from an unselected population but additionally, an intervention given to high risk infants was nested within the study design

Category	Examples
Age at first data	Pre conception cohorts [4], Birth cohorts [1], Childhood cohorts [12]
Inclusion criteria	Unselected cohorts [5, 11, 13–16], inclusion of “high risk infants” (e.g. at least one parent with asthma) [11, 17], inclusion of only patients with asthma [12]
Respiratory specific?	Respiratory and non-respiratory outcomes measured [1, 2], Respiratory/allergy specific [3, 4]
Exposure	Allergen exposure [11], Ambient air quality [18], Breast feeding [19], Maternal diet [20], Maternal illness during pregnancy [21], Smoking [22]