Table 5

A priori versus practical approach: multivariable estimates of risk describing the association between shift length and occupational injury or illness depend on the definition of exposure

A priori approach
N=961 827
Practical approach
N=926 763
Relative risk (95% CI)p ValueRelative risk (95% CI)p Value
≤8 hReferentReferent
>8 and ≤12 h1.43 (1.04 to 1.97)0.031.16 (0.88 to 1.53)0.30
>12 and ≤16 h1.82 (1.17 to 2.82)0.0081.43 (1.05 to 1.95)0.025
>16 and ≤24 h2.29 (1.52 to 3.46)<0.0011.93 (1.33 to 2.81)0.001
>24 h1.68 (0.23 to 12.42)0.612.88 (1.74 to 4.77)<0.001
Continuous (hours)1.04 (1.02 to 1.07)<0.0011.03 (1.02 to 1.04)<0.001
≥10 h1.37 (1.05 to 1.77)0.0181.24 (0.99 to 1.56)0.06
≥12 h1.49 (1.18 to 1.88)0.0011.38 (1.12 to 1.70)0.002
8 h categoryReferentReferent
12 h category1.33 (1.05 to 1.70)0.0181.22 (0.96 to 1.54)0.10
16 h category2.08 (1.12 to 3.86)0.0211.42 (0.99 to 2.05)0.06
24 h category2.05 (1.44 to 2.90)<0.0012.13 (1.54 to 2.96)<0.001
• Each estimate in the table represents a separate multivariable model adjusted for the previously described covariates.

• Estimates between the lines are from different models.