Table 4

Interaction effect of long working hours and ergonomic risk factors on musculoskeletal symptoms

Long working hours (−)*
OR (95% CI): p value
Long working hours (+)†
OR (95% CI): p value
OR for long working hours (−)* vs long working hours (+)† within strata of ergonomic risk factor
OR (95% CI): p value
Ergonomic risk factors (−)Reference1.75 (1.28 to 2.39): <0.0011.75 (1.28 to 2.39): <0.001
Ergonomic risk factors (+)3.49 (3.06 to 3.99): <0.0015.07 (4.33 to 5.93): <0.0011.45 (1.30 to 1.61): <0.000
OR for ergonomic risk factors (−) vs ergonomic risk factors (+) within strata of long working hours3.49 (3.06 to 3.99): <0.0012.89 (2.14 to 3.90): <0.001
Measure of interaction on additive scale: RERI0.82 (0.11 to 1.53): 0.024
Measure of interaction on multiplicative scale: ratio of ORs0.83 (0.50 to 1.14): 0.256
  • Age, sex, education, income, employment and shift work were adjusted for in the model.

  • *Long working hours (−): ≤30 and ≤52 hours.

  • †Long working hours (+): >52 hours.

  • RERI, relative excess risk due to interaction.