Table 1.

Statistics of oxygen concentration and altitude of 2018–2020.

Year	Sample size	Factor	Mean	Max	Min	SD	t test statistics
2018	80	Oxygen concentration (%)	20.19	20.66	19.94	0.16	p < 0.001, 95% CI: 20.15–20.22%
		Altitude (m)	4006	5238	1352	822
2019	166	Oxygen concentration (%)	20.30	20.78	19.98	0.18	p < 0.001, 95% CI: 20.27–20.33%
		Altitude (m)	3000	5026	645	909
2020	176	Oxygen concentration (%)	20.30	20.73	19.97	0.18	p < 0.001, 95% CI: 20.28–20.33%
		Altitude (m)	3562	5362	534	1116