Comparing FEV₁ in Adults in Two Community-Based Studies

¹ From the Department of Environmental Science and Physiology, Harvard School of Public Health, Boston
² From The Channing Laboratory, Brigham and Women's Hospital, Pulmonary Division, Beth Israel Hospital, Harvard Medical School, Boston; and the Department of Epidemiology, State University of Groningen, Groningen, the Netherlands
³ From the Department of Environmental Science and Physiology, Harvard School of Public Health, Boston; The Channing Laboratory, Brigham and Women's Hospital, Pulmonary Division, Beth Israel Hospital, Harvard Medical School, Boston
⁴ From the Department of Epidemiology, State University of Groningen, Groningen, the Netherlands

Data collected in two large-scale longitudinal respiratory studies were analyzed to estimate age-related changes in FEV₁ and to determine the between-study differences in change in FEV₁ among nonsmoking participants. Two adult cohorts in the Netherlands were followed up for 21 years at 3-year intervals and a cohort of adults in 6 cities in the eastern United States was followed up for 6 years. The age distributions and follow-up rate differed for the two studies. The mean rates of decline in FEV₁ for 50-year old male and female never smokers were 27.9±2.8 mL/yr and 22.1±0.9 mL/yr, respectively, in the Netherlands cohort. The estimates for men and women in the Six Cities cohort were 33% and 32% greater, respectively, than those for the Netherlands cohort (p<0.01). The estimated rate of decline in FEV₁ associated with each 1-year increase in age was 0.50±0.12 mL/yr for men and 0.61±0.08 mL/yr for women in the Netherlands cohort. This estimate was comparable for the Six Cities women and the Netherlands women but significantly different for the two cohorts of men. Inclusion of survey (period) effect in the regression model had only a trivial influence on accelerated rate of decline in FEV₁ and did not alter the more rapid acceleration of decline in FEV₁ among the Six Cities men. The present study also showed that use of a "prediction equation" for age adjustment to compare across population samples may produce a biased conclusion if the estimated rate of decline in FEV₁ associated with age is different and the age distributions are different for the two populations. In addition, height adjustment for FEV₁ was found to have a negligible influence on the longitudinal estimates of FEV₁ decline in both study samples. In conclusion, substantial between study variation in decline in FEV₁ occurs despite use of similar data analysis techniques. Differences in the initial age distributions and loss to follow-up appeared to be important factors in this analysis.

Key Words: longitudinal studies • comparison • decline of FEV₁ • model

Submitted on June 9, 1993
Accepted on December 15, 1994

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