Table 3.

Characteristics of participants in reviewed studies

Study	n	n COPD patients	n controls	Age (mean ± SD)	FEV1 (L) (mean ± SD)	FEV1/FVC% (mean ± SD)	Pack-years (mean ± SD)	%Current smoker	% Female
Qiu et al.[23]	1085	620	325	57.3 ± 8.1	N/A	54.4 ± 19.8	41.7 ± 26.2	36.5	45.6
	369	181	109	47.5 ± 7.1	N/A	54.3 ± 21.1	28.7 ± 23.6	27.9	64
Bell et al. [22]	172	N/A	N/A	57.2 ± 8.2	2.46 ± 0.46	N/A	N/A	15.1a	100
Lepeule et al. [25]	756	81 + 42b	N/A	73.3 ± 6.7	2.50 ± 0.6	N/A	20.5 ± 25.7	4	0
Lange et al. [26]	663	107	N/A	72.7 ± 6.7	2.70 ± 0.64	75 ± 8	30.6 ± 24.8	7	0
Marioni et al. [21]	1091	N/A	N/A	69.8 ± 0.78	2.36 ± 0.69	N/A	N/A	N/A	50.4
Wielscher et al. [24]	204	42	27 healthy + 34 GOLD grade 0	53.4± 13.4c	N/A	N/A	N/A	N/A	23.2d

^aValue from entire Twins UK cohort obtained from reference [28]

^bn COPD patients: 81 chronic bronchitis & 42 emphysema

^cInformation provided by the author Wielscher (not available in the original text)

^dInformation provided by the author Wielscher (not available in the original text)