international study of asthma and allergy in childhood phase iii (isaac iii): the role of non-response in valencia

a study was done about non-participation during phase iii of the international study of asthma and allergy in childhood (isaac iii) in valencia to determine whether the non-response rate significantly affected the results obtained in valencia. of the schools selected to participate in isaac iii, 13.3% denied not to, the main reason being they were already participated in a similar study. the isaac iii questionnaire was handed out to participating schools for the parents of 6,358 schoolchildren aged 6-7 years. of these, 53.4% responded correctly. the remaining 46.6% were given a non-response questionnaire (nrq), of which 4.1% completed the questionnaire correctly. the main reason why parents who received the nrq did not participate in isaac iii was that their children had neither asthma nor other atopic disease, so interest was null. no significant statistical differences were observed between the prevalence of asthma in the schoolchildren who participated in isaac iii and in the non-participants who answered the nrq. these results suggest that the isaac iii results relating to asthma are not biased by non-response.