Table 1

Characteristics of cases (active sperm <12×10⁶/ml) and referents (active sperm ⩾12×10⁶/ml) in the Montreal and CITES series

		Montreal				CITES
		Cases						Referents		Cases				Referents
		n	%					n	%	n	%			n	%
Age (y):
⩽30	78	37.5		189	42.4		90	52.3		202	51.0
31–35	74	35.6		124	27.8		58	33.7		130	32.8
>35	56	26.9		133	29.8		24	14.0		64	16.2
All	208	100.0		446	100.0		172	100.0		396	100.0
Clinic year:
1972–76	76	36.2		168	37.7		—	—		—	—
1977–81	65	31.0		139	31.2		—	—		—	—
1982–91	69	32.9		139	31.2		175	100.0		399	100.0
All	210	100.0		446	100.0		175	100.0		399	100.0
Possible lead exposure	37	17.6		81	18.2		44	25.1		114	28.6
No previous pregnancy^1-150	176	84.2		316	71.2^1-165		155	88.6		311	77.9^1-160
Partner ‘normal’	100	47.6		162	36.3^1-160		105	60.0		124	31.1^1-165

↵1-150 Information missing for 1 case and 2 referents in the Montreal study.
↵1-160 p<0.01 cases v referents.
↵1-165 p<0.001 cases v referents.