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Table 4 Pooled risk estimates for breast cancer and heterogeneity analysis from adjusted risk estimates

From: Night-shift work duration and breast cancer risk: an updated systematic review and meta-analysis

Factors stratified Short-term (< 10 years) versus never night-shift work Long-term (≥ 10 years) versus never night-shift work
No. of studies RR (95% CI) \({I}^{2}\), % P value No. of studies RR (95% CI) \({I}^{2}\), % P value
All studies 26 (16, 20–22, 28, 55–75) 1.13 (1.03–1.24) 73.4 0.001 17 (20–22, 28, 55, 58, 62, 64–66, 69–75) 1.08 (0.99–1.17) 42.2 0.028
Study type         
Nested case–control 6 (20, 21, 55–58) 1.40 (0.9–2.19) 66.2 0.011 4 (20, 21, 55, 58) 1.5 (0.86–2.66) 84.7 0.001
Case–control 13 (16, 22, 59–69) 1.25 (1.8–1.44) 59.8 0.003 6 (22, 62, 64–66, 69) 1.22 (1.02–1.46) 0 0.819
Cohort 7 (28, 70–75) 1.02 (0.97–1.06) 0 0.636 7 (28, 70–75) 1.01 (0.95–1.07) 0 0.706
Occupation         
Flight attendants 2 (56, 57) 3.94 (1.42–10.91) 0 0.806 0 - - -
Nurses 4 (58, 67, 68, 73) 1.14 (0.99–1.3) 71.6 0.007 2 (58, 73) 1.25 (0.92–1.70) 81.6 0.004
Other 19 (16, 20–22, 50, 55, 59–66, 69–72, 74, 75) 1.09 (0.97–1.22) 68.8 0.001 14 (20–22, 28, 55, 62, 64–66, 69–72, 74, 75) 1.03 (0.95–1.11) 17.9 0.248
Geographic area         
Europe 17 (16, 20, 28, 55–59, 61, 64–68, 70–72) 1.19 (1–1.41) 72.9 0.001 10 (20, 28, 55, 58, 64–66, 70–72) 1.21 (1.02–1.44) 54.4 0.016
North America 5 (60, 62, 63, 73, 75) 1.04 (0.96–1.13) 39.1 0.145 3 (62, 73, 75) 1.05 (0.94–1.16) 0 0.417
Asia 3 (21, 69, 74) 1.04 (0.93–1.17) 0 0.7 3 (21, 69, 74) 0.94 (0.84–1.07) 16.2 0.303
Oceania 1 (22) 1.25 (1.01–1.55) - - 1 (22) 1.05 (0.78–1.41) - -
Adjusted for reproductive variables         
Yes 24 (16, 20–22, 28, 55–71, 73, 74) 1.15 (1.05–1.27) 72.6 0.001 15 (20–22, 28, 55, 58, 62, 64–66, 69–71, 73, 74) 1.1 (1–1.21) 47.9 0.015
No 2 (72, 75) 0.94 (0.75–1.17) 19 0.266 2 (72, 75) 0.95 (0.76–1.19) 0 0.899
Adjusted for family Hx         
Yes 18 (16, 22, 28, 58–60, 62–69, 71, 73–75) 1.11 (1.03–1.2) 48.7 0.009 12 (22, 28, 58, 62, 64–66, 69, 71, 73–75) 1.1 (1–1.2) 40.2 0.059
No 8 (20, 21, 55–57, 61, 70, 72) 1.16 (0.83–1.62) 83.5 0.001 5 (20, 21, 55, 70, 72) 1.06 (0.84–1.34) 44.1 0.128
Adjusted for confounders         
Yes 25 (16, 20–22, 28, 55, 57–75) 1.13 (1.03–1.23) 71.9 0.001 17 (20–22, 28, 55, 58, 62, 64–66, 69–75) 1.08 (0.99–1.17) 42.2 0.028
No 1 (57) 3.27 (0.54–19.85) - - 0 - - -
Quality category         
High 21 (16, 20, 22, 28, 58–70, 72–75) 1.15 (1.04–1.26) 73.8 0.001 14 (20, 22, 28, 58, 62, 64–66, 69, 70, 72–75) 1.1 (1–1.21) 41.4 0.042
Moderate 5 (21, 55–57, 71) 1.05 (0.78–1.40) 50.2 0.09 3 (21, 55, 71) 1.01 (0.82–1.24) 45.3 0.161
Source of funding         
Low risk 22 (16, 20–22, 28, 56–60, 62, 64–73, 75) 1.08 (1.01–1.17) 50.2 0.003 15 (20–22, 28, 58, 62, 64–66, 69–73, 75) 1.09 (1–1.2) 46 0.02
Unclear 4 (55, 61, 63, 74) 1.36 (0.97–1.91) 79.9 0.002 2 (55, 74) 1.02 (0.66–1.58) 16.7 0.273
  1. CI confidence interval
  2. P values represent heterogeneity