Table 2.

Incidence rate (IR) and incidence rate ratio (IRR) of on-duty, long-term injury leave (≥90 days) by shift, Buffalo Cardio-metabolic Occupational Police Stress (BCOPS) Study, 2004–2009. [95% CI=95% confidence interval]

Shift	Number at risk a	Person hours b	Number injured c	IR per 100 000 person hours d	95% CI e for IR	Unadjusted		Age- and gender-adjusted
						IRR	95% CI	IRR	95% CI
Day	412	2512333	12	0.48	0.27–0.86
Afternoon	405	1891469	11	0.59	0.15–2.37
Night	373	1273236	17	1.33	0.36–5.00
Night versus day						2.76	1.30–5.83	3.12	1.35–7.21
Afternoon versus day						1.21	0.53–2.77	1.42	0.54–3.71
Night versus afternoon						2.27	1.06–4.87	2.21	1.04–4.68

^aThe number of participants who contributed person-hours to that specific shift. Note that a participant can contribute person-hours to one, two, or all three shifts but first serious injury occurs in only one of the three shifts.

^bThe total number of hours of work at regularly scheduled time for each shift. This is the total time (in hours) at risk for first serious injury.

^cThe number of participants with first long-term injury (note that there were 13 officers with long-term injury who dominantly worked on afternoon shift (see table 1) but two of those were first injured while working on night shift leading to 11 cases for afternoon shift and 17 (15+2) cases for the night shift.

^dIR is computed as the number of participants with first serious injury divided by total person-hours for the shift and the result expressed in 100 000 working hours.

^eThe 95% CI were computed using the Poisson regression model for ungrouped data.