Table 2—

Comparison of multiple regression models between the original sample^# and the external validation sample^¶

	Original		External validation
	OR⁺	p-value	Subjects n	OR (95% CI)⁺	p-value
Age group yrs
40–49^§	1.00		276	1.00
50–59	2.20	0.022	265	1.99 (1.38–2.88)	<0.001
60–69	4.73	<0.001	133	2.92 (1.85–4.61)	<0.001
≥70	7.77	<0.001	2	NA	NA
BMI kg·m⁻²
<25.4^§	1.00		386	1.00
25.4–29.7	0.44	0.002	191	0.66 (0.45–0.97)	0.033
>29.7	0.35	<0.001	99	0.57 (0.35–0.94)	0.026
Smoking history pack-yrs
<15^§	1.00		26	1.00
15–24	1.63	0.112	106	0.74 (0.29–1.92)	0.537
25–49	1.99	0.010	367	1.11 (0.46–2.63)	0.822
≥50	4.05	<0.001	177	1.66 (0.67–4.10)	0.271
Weather affects cough^ƒ	1.68	0.089	138	0.87 (0.58–1.31)	0.502
Phlegm without a cold^ƒ	1.81	0.013	486	1.47 (0.7–2.22)	0.068
Phlegm in the morning^ƒ	0.54	0.022	253	0.67 (0.46–0.99)	0.045
Wheeze^##	2.08	0.001	535	1.74 (1.14–2.68)	0.011
Present/previous allergies^ƒ	0.52	0.005	154	0.98 (0.67–1.47)	0.994

Original sample data from 9. OR: odds ratio; CI: confidence interval; BMI: body mass index; NA: not applicable (insufficient number of cases in category). ^#: n = 798; ^¶: n = 676; ⁺: for having chronic obstructive pulmonary disease (COPD; i.e. forced expiratory volume in one second (FEV₁)/forced vital capacity (FVC) of <0.70 with respiratory symptoms) versus not having COPD (i.e. FEV₁/FVC of ≥0.70); ^§: reference; ^ƒ: yes versus no; ^##: any versus never.