Table 2. Summary of pooled odds ratios of MDS for ever vs. never smoking in subgroups.

subgroup	Number of studies	Pooled OR (95%CI)	Q-test for heterogeneity P value (I2 score)	Egger’s test P value
Geographical region
United States	3 (9, 13, 22)	1.84 (1.30, 2,06)	0.081 (60.3%)	0.217
Asia	3 (10, 17, 19)	1.14 (0.85, 1.53)	0.254 (27.0%)	0.542
Europe	8 (11, 12, 14, 15, 16, 18, 20, 21)	1.40 (1.18, 1.67)	0.648 (0%)	0.194
Sex
Men	3 (13, 17, 19)	1.29 (0.95, 1.77)	0.879 (0%)	0.389
women	2 (13, 19)	2.02 (1.24, 3.31)	0.820 (0%)	-
MDS subtype
RA/RARS	3 (13, 16, 19)	2.23 (1.50, 3.30)	0.889 (0%)	0.738
RAEB/RAEBt	4 (10, 13, 16, 21)	1.59 (1.21, 2.10)	0.771 (0%)	0.486
No. of cigarettes
= 0	7 (9, 10, 11, 16, 17, 18, 20)	1	-	-
<20 and >0	6 (9, 10, 16, 17, 18, 20)	1.36 (1.13, 1.64)	0.278 (19.9%)	0.883
≥20	6 (9, 10, 11, 17, 18, 20)	1.62 (1.03, 2.55)	<0.01 (78.1%)	0.492
Duration
= 0	5 (10, 11, 12, 16, 17)	1	-	-
<20 and >0	3 (10, 11, 17)	1.02 (0.66, 1.56)	0.533 (0%)	0.321
≥20	5 (10, 11, 12, 16, 17)	1.38 (0.90, 2.13)	0.011 (69.3%)	0.86
Pack-years
= 0	5 (10, 11, 15, 16, 21)	1	-	-
<20 and >0	5 (10, 11, 15, 16, 21)	1.13 (0.88, 1.46)	0.216 (29.2%)	0.114
≥20	5 (10, 11, 15, 16, 21)	1.94 (1.29, 2.92)	0.038 (57.5%)	0.170

RA: refractory anemia; RARS: RA with ringed sideroblasts; RAEB: RA with excess blasts (RAEB); RAEBt: RAEB in transformation.