Lower respiratory tract symptoms in Queensland schoolchildren. The questionnaire: its reliability and validity.

Respiratory symptoms and ventilatory function were recorded on 4549 Queensland schoolchildren. Previously parents of 67 children on two occasions showed that key questions on wheezy breathing and productive cough were reliable, with agreement of responses in 97% and 91% of subjects. These two questions divided the children into four main groups: Group A, those children with attacks of asthma or of wheezy breathing; Group B, those with attacks of cough with sputum; Group AB, those with both symptoms; and Group N, those with neither symptom. The validity of the questionnaire was examined by relating question responses to ventilatory function expressed as normalized residuals. Mean (+/- SD) normalized FEF 25-75 residuals for the major groups were: N, 0 +/- 1.00; B, -0.10 +/- 1.00; A, -0.26 +/- 1.10; and AB, -0.50 +/- 1.07. In subjects with wheeze, residuals distinguished subjects on a basis of frequency of wheeze, total number of attacks, and the association with breathlessness. The proportion of eight year olds in each group (N, B, A and AB) was 44%, 33%, 2.6%, and 20.5% respectively; and of twelve year olds, 52%, 28%, 2.7%, and 18.1%. These results contrast with those of a comparable survey of Tasmanian seven year olds where the proportion was 51%, 33%, 1.8%, and 14.4% respectively.