1991 Volume 26 Issue 5 Pages 333-339
We measured forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and maximal expiratory flow rates at 50% and 25% FVC (Vmax50, Vmax25) of school children three times at intervals of two years to estimate between-and within-subject variability of those measurements in the follow-up period. The initial sample was composed of 217 boys and 224 girls. One hundred and seventy three boys and 171 girls performed acceptable measurements at all of three surveys.
Two simple models for repeated measurements explained the distribution of pulmonary function data quite well. Coefficients of determination of the models were more than 0.95 for FVC and FEV1, and were more than 0.85 for Vmax50 and Vmax25. Estimated between-subject variability of pulmonary function was two to four times greater than within-subject variability both in boys and girls. Summation of longitudinally estimated between-and within-subject variability was comparable with cross-sectionally estimated error variance for all of the pulmonary function indices.
From these results, we concluded that longitudinal analysis of a series of observations must be superior to crosssectioral analysis of a single examination when we study normal growth patterns of children or possible risk factors which might give a change to the course of development of pulmonary function in childhood.
