Table 1. Relationship between normal cranial bone marrow typing and age at 2,000–3,000 m above sea level.

Age group (years)	Bone marrow type, n (%)						Diploe thickness (mm)
	Ia	Ib	II	IIIa	IIIb	IV
0–5	26 (32.5)	34 (42.5)	20 (25.0)	0 (0.0)	0 (0.0)	0 (0.0)	1.72±0.69
6–14	2 (2.0)	16 (16.0)	39 (39.0)	6 (6.0)	37 (37.0)	0 (0.0)	2.75±0.93
15–29	0 (0.0)	0 (0.0)	7 (7.0)	7 (7.0)	66 (66.0)	20 (20.0)	3.86±0.85
30–49	0 (0.0)	0 (0.0)	5 (5.0)	9 (9.0)	71 (71.0)	15 (15.0)	4.12±1.20
≥50	0 (0.0)	0 (0.0)	0 (0.0)	11 (13.8)	20 (25.0)	49 (61.3)	4.34±1.00
χ2/F (P)	481.638 (0.000)						113.039 (0.000)
r (P)	0.739 (0.000)						0.673 (0.000)