Table 2. Relationship between normal cranial bone marrow typing and age at 3,100–4,000 m above sea level.

Age group (years)	Bone marrow type, n (%)						Diploe thickness (mm)
	Ia	Ib	II	IIIa	IIIb	IV
0–5	20 (33.3)	29 (48.3)	11 (18.3)	0 (0.0)	0 (0.0)	0 (0.0)	1.85±0.67
6–14	5 (6.3)	15 (18.8)	40 (50.0)	4 (5.0)	16 (20.0)	0 (0.0)	2.88±0.99
15–29	0 (0.0)	0 (0.0)	9 (11.3)	4 (5.0)	58 (72.5)	9 (11.3)	3.87±1.02
30–49	0 (0.0)	0 (0.0)	6 (7.5)	8 (10.0)	60 (75.0)	6 (7.5)	3.93±0.91
≥50	0 (0.0)	0 (0.0)	0 (0.0)	10 (16.7)	13 (21.7)	37 (61.7)	4.31±0.89
χ2/F (P)	441.959 (0.000)						76.104 (0.000)
r (P)	0.772 (0.000)						0.635 (0.000)