Table 4.

Yearly crude and adjusted BSI rates by institution in each study phase. Adjusted rates were determined using generalised estimating equation (GEE) models for Poisson regression adjusted for age and accounting for within-subject correlation, using data across all phases of the study at once to make years comparable

	Institution 1						Institution 2
Phase	N	BSI events	Person-years	Crude rate	Adjusted rate	95% CI	N	BSI events	Person-years	Crude rate	Adjusted rate	95% CI
Historical
Year 1	21	13	17.7	0.73	0.77	0.48 to 1.21	14	5	12.2	0.41	0.36	0.14 to 0.95
Year 2	23	9	20.2	0.45	0.46	0.22 to 0.95	13	5	12.0	0.42	0.35	0.12 to 1.08
Year 3	22	14	19.9	0.70	0.70	0.38 to 1.26	9	2	8.2	0.24	0.22	0.02 to 2.11
Total	36	36	57.8	0.62	0.63	0.46 to 0.87	20	12	32.3	0.37	0.33	0.16 to 0.68
Pilot
Year 1	17	3	16.7	0.18	0.17	0.05 to 0.60	13	2	11.9	0.17	0.21	0.07 to 0.63
Year 2	19	13	16.5	0.79	0.73	0.39 to 1.38	15	6	13.3	0.45	0.35	0.16 to 0.80
Year 3	22	10	18.1	0.55	0.56	0.34 to 0.92	22	9	18.7	0.48	0.37	0.15 to 0.92
Total	31	26	51.3	0.51	0.49	0.33 to 0.71	35	17	43.8	0.39	0.32	0.17 to 0.59
Intervention*
Year 1	21	8	19.0	0.42	0.43	0.19 to 0.99	28	23	23.7	0.97	0.86	0.51 to 1.47
Year 2	19	5	16.5	0.30	0.31	0.14 to 0.65	24	8	21.6	0.37	0.31	0.13 to 0.75
Year 3	18	3	16.3	0.18	0.19	0.07 to 0.52	20	7	18.2	0.38	0.35	0.14 to 0.86
Year 4	16	1*	10.4	0.10	0.10	0.01 to 0.68	20	7	11.5	0.61	0.66	0.35 to 1.25
Total	34	17	62.2	0.27	0.27	0.17 to 0.44	44	45	75.1	0.60	0.56	0.37 to 0.86

*P value-for-interaction for institution and historical versus intervention=0.0086; p value for historical versus intervention at Institution 1=0.041; p value for historical versus intervention at Institution 2=0.20

BSI, bone stress injury .