Measurement of functional severity of asthma in children.

The usefulness of surveys for measuring the severity of asthma in school-age children depends on the availability of reliable and valid questionnaires. The aim of this study was to develop a measure of functional severity of asthma over the previous 12 mo, for use in population studies and in investigating treatment regimens. Of 10,198 children surveyed, 9,192 (90%) in school Years 2, 7, and 10 (mean ages 8, 13, and 16 yr) in Melbourne were screened for wheeze. The parents of the 1,267 children with wheeze were interviewed. Symptoms and restriction of activity due to asthma were analyzed using factor analysis and the partial credit version of the item response theory measurement model. The result was a continuous severity scale that was highly consistent with the data, and with goodness of fit statistics indicating the severity of 97% of children was well described by the scale. The scale correlated significantly with school absence due to wheeze (r = 0.35), functional impairment during the 2 wk before interview (Functional Status II-R [FSII-R], r = 0.30), visits to medical care for wheeze (r = 0.22), and amount of medication (r = 0.36). For descriptive purposes, a simple index with four bands of severity was developed from the continuous severity scale: low severity (47% of children with wheeze), moderate (30%), mild (18%), and high (5%). The scale and index facilitate standardized description of the impact of asthma on daily life on the basis of responses to six survey questions.