Phase One Methodology

ISAAC Phase One was a multi-centre multi-country cross sectional study involving 2 age groups of school children, 13-14 year old (adolescents) and 6-7 year old.(children) Schools were randomly selected from a defined geographical area. Written questionnaires on asthma, rhinitis and eczema symptoms (translated from English) were completed by the adolescents at school, and at home by the parents of the children. An asthma symptoms video questionnaire for the adolescents was optional. A sample size of 3000 per age group was used to give sufficient power (90% at a 1% significance level), and a high participation rate was a requirement. In Phase One over 700,000 children were involved. Field work was conducted in the majority of centres between 1994 and 1995. Data was then sent to the International Data Centre in Auckland, New Zealand, where the methodology was checked and the data analysed.

Phase One used simple core written questionnaires for two age groups, and was completed in 156 collaborating centres in 56 countries with a total of 721,601 children participating. In the 13-14 year age group 155 centres from 56 countries participated, of which 99 centres completed a video questionnaire. For the 6-7 year age group there were 91 collaborating centres in 38 countries. ISAAC Phase One demonstrated a large variation in the prevalence of asthma symptoms in children throughout the world including hitherto unstudied populations. It is likely that environmental factors were responsible for the major differences between countries. The results provided a framework for studies between populations in contrasting environments to pursue new clues about the aetiology of asthma. Ecological studies were undertaken using the Phase One data to develop hypotheses about environmental factors.

Fuller details of Phase One are published in the Phase One Manual and in a paper in the European Respiratory Journal.