Table 1

Study population characteristics: number of births by plant employees conceived after starting employment, by parents’ demographic characteristics

	Fathers employed at plant (n=127)			Mothers employed at plant (n=21)
	Girls (n)	Boys (n)	Sex ratio	Girls (n)	Boys (n)	Sex ratio
	137	167	0.55	21	30	0.59
Year of birth
<1970	21	14	0.40
70–80	54	61	0.53	5	14	0.74
80–90	42	61	0.59	13	12	0.48
>1990	20	31	0.61	3	4	0.57
Age of parent (employed at plant) at birth
<25	19	20	0.51	3	11	0.79
25–30	47	56	0.54	7	6	0.46
30–40	59	80	0.58	9	11	0.55
≥40	12	11	0.48	2	2	0.50
Age of other parent at birth
<25	33	44	0.57
25–30	47	51	0.52
30–40	30	43	0.59
≥40	3	1	0.25
Unknown	24	28	0.54	21	30	0.59
Age at start of employment
23–30	26	39	0.60	7	6	0.46
30–37	47	66	0.58	8	11	0.58
>37	64	62	0.49	6	13	0.68