Age group (years) | Control group | Intervention group | Intervention relative to control group | ||||||||
N | Slips | Person-hours | Crude incidence rate* (95% CI) | aIRR† (95% CI) | N | Slips | Person- hours | Crude incidence rate* (95% CI) | aIRR‡ (95% CI) | P value | |
<30 | 378 | 721 | 169 091 | 0.160 (0.148 to 0.172) | 1.00 (ref) | 389 | 641 | 166 475 | 0.144 (0.133 to 0.156) | 0.93 (0.73 to 1.20) | 0.585 |
30–39 | 487 | 919 | 220 639 | 0.156 (0.146 to 0.167) | 1.18 (0.94 to 1.48) | 475 | 464 | 209 920 | 0.083 (0.076 to 0.091) | 0.58 (0.46 to 0.74) | <0.001 |
40–49 | 632 | 1218 | 292 666 | 0.156 (0.147 to 0.165) | 1.32 (1.06 to 1.64) | 616 | 685 | 277 148 | 0.093 (0.086 to 0.100) | 0.53 (0.43 to 0.64) | <0.001 |
50–59 | 633 | 1023 | 291 799 | 0.131 (0.124 to 0.140) | 1.00 (0.80 to 1.25) | 677 | 741 | 306 812 | 0.091 (0.084 to 0.097) | 0.69 (0.57 to 0.85) | <0.001 |
60+ | 117 | 229 | 50 983 | 0.168 (0.147 to 0.192) | 2.00 (1.40 to 2.87) | 100 | 102 | 41 603 | 0.092 (0.075 to 0.112) | 0.39 (0.24 to 0.64) | <0.001 |
*Per 37.5 person-hours (also known as one full-time working week).
†aIRRs comparing age groups among the control group only, estimated using mixed-effects negative binomial regression with sex, prerandomisation slip rate and job role as fixed effects, and site as random effect.
‡aIRRs comparing the intervention group to control group by age, estimated using mixed-effects negative binomial regression with sex, prerandomisation slip rate, job role, group allocation, and the interaction between group allocation and age as fixed effects, and site as random effect.
aIRR, adjusted incidence rate ratio; N, number of people; ref, reference category.