Based on the 1990 questionnaire which had been developed de novo, a new questionnaire was designed in 1998 that has been used in similar form in all subsequent surveys. Compared to the 1990 questionnaire, the new questionnaire included further questions on symptoms (e.g. upper respiratory symptoms) and environmental exposures. Some questions were also adapted to the wording used in International Study of Asthma and Allergies in Childhood (ISAAC).

The information collected includes

1. Wheeze and cough:

• Wheeze ever and age at onset
• Frequency and duration of wheeze attacks in the last 12 months
• Triggers of wheeze such as colds, exercise, foods, beverages, pollen, house dust etc.
• Interference with sleep and speech limitation due to wheeze
• Occurrence of cough with or apart from colds
• Triggers of cough such as colds, exercise, foods, beverages, pollen, house dust etc.
• Doctor diagnosed asthma or bronchitis
• Childs history of pneumonia, whooping cough, bronchiolitis, and other chest infections

2. Ear, nose, throat symptoms:

• Frequency of colds or flu in the past 12 months
• Problems with sneezing, running or blocked nose, snoring, in the past 12 months
• Interference of these symptoms with daily activities and sleep
• Prevalence of ear infections, throat infections, and croup in the past 12 months

3. Treatment and Healthcare:

• Hospitalization and frequency of GP visits due to wheezing symptoms
• Use of asthma medication, use of inhalers

4. Environment:

• Attendance of day care, nursery or play school
• Fuel used for heating and for cooking
• Contact with animals
• Sibship and household structure
• Smoking exposure
• Parent’s history of wheezing, asthma, bronchitis, hayfever, eczema
• Self-assessed ethnicity and main language spoken
• Education, work
• Physical activities
• Traffic density at home