. Author manuscript; available in PMC: 2016 Jan 1.

Published in final edited form as: Cancer Causes Control. 2014 Nov 25;26(1):143–150. doi: 10.1007/s10552-014-0493-0

Table 6.

Joint effects of shift work and magnetic field exposure on risk of breast cancer (1709 cases and 4780 controls)

Stratified group^*	Cases	HR^a	95% CI
Entire employment period
MF ≤ 6.24 μT-yrs and shift work duration ≤ 27.5 yrs	1101	1.00	(ref)
MF ≤ 6.24 μT-yrs and shift work duration > 27.5 yrs	165	0.94	(0.77, 1.14)
MF > 6.24 μT-yrs and shift work duration ≤ 27.5 yrs	299	1.02	(0.88, 1.19)
MF > 6.24 μT-yrs and shift work duration > 27.5 yrs	122	0.87	(0.70, 1.08)
*Redefined shift work groups*
MF ≤ 6.24 μT and shift work = 0	467	1.00	(ref)
MF ≤ 6.24 μT and shift work > 0	799	0.92	(0.81, 1.06)
MF > 6.24 μT and shift work = 0	73	0.91	(0.68, 1.22)
MF > 6.24 μT and shift work > 0	348	0.94	(0.80, 1.11)

MF: Magnetic fields. The cutoff points for categories were defined by the values at the 75^th percentiles for the duration of years working on night-shift work and cumulative exposure of MF (μT -years)

HR: Hazard Ratio; 95% CI: confidence interval