Age of onset
Age of onset was defined as the mid-point of the age bracket in which presence was first reported. For example, if eczema presence was first reported in the period 4– 7 years, age of eczema onset was taken as 5.5 years. In cases of age brackets where the end was defined as ageQ, the age of onset represented the mid-point of the age at start of the period and ageQ (4 years – ageQ, age 5 at time of questionnaire, age of onset: 4.5 years).