Table 1. The demographics and clinical characteristics of the sample.

Variables (mean±SD)	HC		MDD		t(F)/χ2	p-value
Sex(male/female)	41/71		42/78		0.065	0.891 a
Age (years)	30.29±6.99		30.58±7.41		0.296	0.768 b
Years of education	15.42±3.82		12.18±4.20		-6.139	0.000 b
HDRS score	0.47±0.69		23.47±4.54		53.064	0.000 b
GMV(mm3)	619.11±60.64		608.68±55.99		-1.363	0.580
	Young HC	Old HC	EOD	LOD
Sex(male/female)	25/35	16/36	27/31	15/47	8.025	0.046 c
Age (years)	24.63±2.37	36.83±4.33	23.98±2.89	36.74±4.38	\	0.000 d
Age onset (years)	\	\	23.23±2.97	36.06±4.53	\	0.000 b
Illness duration(months)	\	\	8.98±7.06	8.24±7.89	0.539	0.591 b
Years of education	16.57±2.34	14.09±4.71	14.00±3.41	10.47±4.17	27.586	0.000 e
HDRS score	0.42±0.65	0.54±0.75	22.91±4.19	23.98±4.82	-1.295	0.198 f
GMV(mm3)	637.27±60.14	598.16±54.64	629.71±51.61	589.01±53.05	10.870	0.000 g

MDD = major depressive disorder; EOD = early adult onset depression; LOD = later adult onset depression; HC = healthy control; HDRS = Hamilton Rating Scale for Depression.

^a The p-value for sex distribution in the two groups was obtained by chi-square test.

^b The p-values were obtained by two sample t-test.

^c The p-values for sex distribution among the four groups was obtained by chi-square test p = 0.711(Young HC vs EOD), p = 0.432(Old HC vs LOD).

^d The p-values were obtained by one-way analysis of variance tests. Post hoc t-test: p = 0.184(EOD vs Young HC), p = 0.918(LOD vs Older HC).

^e The p-values were obtained by one-way analysis of variance tests. Post hoc t-test: p = 0.000(EOD vs Young HC), p = 0.000(LOD vs Older HC), p = 0.000(EOD vs LOD).

^f The p-values were obtained by two sample t-test.

^g The p-values were obtained by one-way analysis of variance tests. Post hoc t-test: p = 0.342(EOD vs Young HC), p = 0.705 (LOD vs Older HC).