Table 3. Prevalence rates and adjusted odds ratios for having chronic bronchitis, according to spirometric category and age group.

Spiometric Category a	N b	No. (%) of participants with chronic bronchitis c	Adjusted odds ratio (95% CI) d
Age 40-80
Normal	5,684	599 (10.5)	1.00
Airflow-obstruction	891	208 (23.3)	1.92 (1.62, 2.29)
Restrictive-pattern	434	69 (15.9)	1.39 (1.08, 1.78)
Age 40-64
Normal	3,787	356 (9.4)	1.00
Airflow-obstruction	515	118 (22.9)	2.13 (1.70, 2.66) e
Restrictive-pattern	276	37 (13.4)	1.35 (0.93, 1.97) f
Age 65-80
Normal	1,897	243 (12.8)	1.00
Airflow-obstruction	376	90 (23.9)	1.83 (1.45, 2.32) e
Restrictive-pattern	158	32 (20.3)	1.51 (1.10, 2.06) f

Abbreviations: FEV1, forced expiratory volume in 1-second; FVC, forced vital capacity; GLI, Global Lung Function Initiative; GLI-LLN₅, lower limit of normal at the 5^th percentile distribution, as defined by a GLI-calculated Z-score of -1.64; SD, standard deviation.

^aNormal spirometry was defined by FEV1/FVC and FVC, both ≥GLI-LLN₅; airflow-obstruction by FEV1/FVC<GLI-LLN₅; and restrictive-pattern by FEV1/FVC≥GLI-LLN₅ and FVC<GLI-LLN₅.

^bVaried from Table 1 because of missing data.

^cPercentage of the corresponding spirometric category.

^dOdds ratios were calculated using logistic regression models, adjusted for age, height, sex, ethnicity, BMI, smoking history, high cardiovascular risk, and health status.

^eNot significantly different in the age group of 40-60 vs. 65-80 (p-value for age interaction was .208).

^fNot significantly different in the age group of 40-60 vs. 65-80 (p-value for age interaction was .290).