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).