Table 2.

Pooled SMD of plasma Hcy levels in PD patients and controls in subgroup analysis.

Subgroups		No. of studies	Sample size	SMD and 95% CI	p value	Test of heterogeneity I2 (%)	Egger’s test for publication bias
							t	P value
Sample size
	<100	6	454	0.74 [0.43, 1.06]	<0.001	60	0.94	0.3476
	≥100	17	3,897	0.90 [0.57, 1.23]	<0.001	95	1.57	0.1175
Sex
	Male*	3	307	0.61 [0.38, 0.66]	<0.001	0	−1.57	0.1172
	Female*	3	503	0.48 [0.30, 0.66]	<0.001	44	0.52	0.6015
Age
	~60*	2	61	0.07 [−0.43, 0.57]	0.79	0	/	/
	60 ~ 70	18	3,439	0.82 [0.47, 1.18]	<0.001	95	0.80	0.4264
	70 ~ 80	8	962	0.92 [0.62, 1.22]	<0.001	75	−0.99	0.3223
	80~*	2	46	0.93 [0.32, 1.55]	0.003	0	/	/
Region
	China	5	1,106	1.15 [0.14, 2.16]	0.03	98	−0.49	0.6242
	Korea*	3	563	0.51 [0.32, 0.69]	<0.001	6	−0.52	0.6015
	Europe	11	2,206	0.88 [0.65, 1.12]	<0.001	84	1.95	0.0516
Hhcy
	Yes	3	139	2.02 [1.26, 2.78]	<0.001	63	3.00	0.1172
	No	3	182	−0.04 [−0.52, 0.60]	0.90	71	−0.52	0.6015
Levodopa therapy
	Yes	19	3,280	0.87 [0.69, 1.06]	<0.001	82	1.85	0.0637
	NO*	4	536	0.41 [0.19, 0.62]	<0.001	14	0.00	1.0000
cognitive function
	PDD or CI	6	1,103	1.11 [0.81, 1.40]	<0.001	74	1.32	0.1885
	No	5	1,108	0.55 [0.15, 0.95]	0.007	89	0.98	0.3272
H and Y
	1 ~ 2	4	599	1.63 [−0.83, 4.10]	0.19	95	−0.68	0.4969
	2 ~ 3*	8	1,374	3.54 [3.07, 4.01]	<0.001	16	0.49	0.6207
	4 ~ 5	2	119	5.37 [3.20, 7.54]	<0.001	91	/	/

Hhcy, Hyperhomocysteinemia. PDD, Parkinson’s Disease with dementia. H and Y, Hoehn and Yahr Stage. * the fix-effect model was applied in the subgroup analysis.