Table 4 Association between proportion of night shifts and musculoskeletal pain and headaches among nurses working 3-shift schedule (n = 551). Incidence rate ratio (IRR) with 95% confidence intervals (CI) and p-values from negative binomial regression analysis

Proportion of night shifts (%)

Neck-, shoulder-, and upper back pain

  < 25

366

1.00 (ref.)

1.00 (ref.)

 25–49.9

144

0.96 (0.75, 1.23)

0.96 (0.75, 1.23)

  ≥ 50

41

0.97 (0.64, 1.46)

0.96 (0.64, 1.46)

Proportion of night shifts (%)

Low back pain

  < 25

366

1.00 (ref.)

1.00 (ref.)

 25–49.9

144

0.85 (0.64, 1.13)

0.87 (0.65, 1.16)

  ≥ 50

41

0.74 (0.46, 1.20)

0.74 (0.45, 1.19)

Proportion of night shifts (%)

Pain in the upper extremities

  < 25

366

1.00 (ref.)

1.00 (ref.)

 25–49.9

144

0.71 (0.47, 1.08)

0.77 (0.51, 1.15)

  ≥ 50

41

0.67 (0.33, 1.35)

0.64 (0.32, 1.27)

Proportion of night shifts (%)

Pain in the lower extremities

  < 25

366

1.00 (ref.)

1.00 (ref.)

 25–49.9

144

0.92 (0.69, 1.22)

0.94 (0.71, 1.24)

  ≥ 50

41

0.74 (0.46, 1.19)

0.70 (0.44, 1.13)

Proportion of night shifts (%)

Headache

  < 25

366

1.00 (ref.)

1.00 (ref.)

 25–49.9

144

1.07 (0.87, 1.30)

1.03 (0.85, 1.26)

  ≥ 50

41

1.02 (0.73, 1.42)

1.02 (0.73, 1.41)