Table 4.

Risk of Breast Cancer in Relation to Cumulative Magnetic Field Exposure at Work for Cases Stratified by Age at Diagnosis, Shanghai, China, 1989–2000

Cumulative Exposure, μT-years	No. of Cases	HRa	95% CI
	Diagnosed at <50 Years of Age (n = 727)
Entire employment period
>0–2.37	181	1.00	Referent
>2.37–3.48	182	1.34	1.06, 1.69
>3.48–4.83	181	1.32	1.03, 1.69
>4.83	183	0.96	0.75, 1.22
P for trendb		0.193
10-year lag
>0–2.37	419	1.00	Referent
>2.37–3.48	134	0.94	0.75, 1.17
>3.48–4.83	56	0.85	0.62, 1.16
>4.83	88	0.79	0.60, 1.04
P for trend		0.041
20-year lag
>0–2.37	419	1.00	Referent
>2.37–3.48	19	0.61	0.38, 1.00
>3.48–4.83	14	0.99	0.56, 1.75
>4.83	17	0.56	0.33, 0.96
P for trend		0.024
Since the year of 1965
>0–2.37	181	1.00	Referent
>2.37–3.48	183	1.34	1.06, 1.69
>3.48–4.83	181	1.32	1.03, 1.69
>4.83	182	0.96	0.75, 1.22
P for trend		0.193
	Diagnosed at ≥50 Years of Age (n = 960)
Entire employment period
>0–3.22	240	1.00	Referent
>3.22–4.75	240	0.98	0.78, 1.22
>4.75–7.12	240	1.11	0.89, 1.39
>7.12	240	1.06	0.85, 1.32
P for trendb		0.496
10-year lag
>0–3.22	286	1.00	Referent
>3.22–4.75	243	0.89	0.71, 1.10
>4.75–7.12	210	1.07	0.86, 1.33
>7.12	219	1.00	0.81, 1.25
P for trend		0.553
20-year lag
>0–3.22	461	1.00	Referent
>3.22–4.75	191	0.91	0.74, 1.10
>4.75–7.12	141	1.31	1.04, 1.65
>7.12	151	0.97	0.77, 1.22
P for trend		0.892
Since the year of 1965
>0–3.22	513	1.00	Referent
>3.22–4.75	205	1.01	0.81, 1.25
>4.75–7.12	115	1.36	1.01, 1.82
>7.12	118	0.92	0.70, 1.19
P for trend		0.693

Abbreviations: CI, confidence interval; HR, hazard ratio.

^a Adjusted for age at the beginning of follow-up as a continuous variable.

^b Trend tests used the median values of each quartile as the score variable.