Supplementary Table 1.

Descriptive statistics on the four common semen quality parameters

Group	Normal group (n=9686)	Abnormal group (n=29 218)	Total (n=38 905)
Percentage of fast forward motile spermatozoa (%)	48.10 (41.90, 55.10)	31.30 (25.00, 46.40)	36.10 (25.00, 46.40)
Percentage of total forward motile spermatozoa (%)	64.80 (57.80, 72.05)	45.90 (34.40, 56.20)	51.30 (40.10, 62.90)
Percentage of sperm with normal morphology (%)	6.90 (5.30, 9.50)	2.60 (1.30, 4.30)	3.60 (1.70, 6.20)
Semen volume (ml)	3.11 (1.28)	2.95 (1.75)	2.99 (1.65)

Data of percentage of fast forward motile spermatozoa, percentage of total forward motile spermatozoa, and percentage of spermatozoa with normal morphology presented as median (first quartile, third quartile), while for semen volume presented as mean (s.d.). s.d.: standard deviation