Sources of variation in forced expiratory volume in one second and forced vital capacity.

Published prediction equations for lung function differ considerably, but the components of population variation responsible for the differences are unknown. Data were analysed for 6,323 never-smoking adults who did not report wheeze or asthma, from 42 centres participating in the European Community Respiratory Health Survey. Means and components of variance were estimated for males and females aged 20-24 yrs, and the relationships with age and height were examined in those aged 25-44 yrs. Mean lung function for those aged 20-24 yrs differed between centres, but variation could not be wholly attributed to differences in population or equipment. The maximum difference in means by equipment type was 101 mL for FVC in males. Equipment differences were not statistically significant adjusted for country, but differences in mean forced expiratory volume in one second and forced vital capacity by country, adjusted for instrument, were statistically significant in males. Differences between centres in relation to age and height had less influence on predicted values. In conclusion, there are unexplained differences in lung function between ethnically similar nonsmoking symptom-free populations. Neither national reference curves nor those based on the same ethnic group can be guaranteed to give accurate norms of lung health.