Table 2

Rate ratios of standardised mortality ratio from Poisson regression model

Variables	Primary hip replacements			Primary knee replacements
Variables	Rate ratio	95% CI	P value	Rate ratio	95% CI	P value
Gender
Female	Ref			Ref
Male	0.96	0.91 to 1.02	0.216	1.03	0.97 to 1.10	0.308
Ethnicity
European/others	Ref			Ref
Māori	1.61	1.46 to 1.78	<0.001	1.71	1.52 to 1.92	<0.001
Pacific	0.96	0.67 to 1.39	0.829	0.98	0.79 to 1.22	0.883
Asian	1.00	0.62 to 1.61	0.997	0.78	0.61 to 0.99	0.045
Age (years)
<40	Ref			Ref
40–49	0.72	0.31 to 1.69	0.451	0.29	0.07 to 1.28	0.102
50–59	0.75	0.34 to 1.70	0.494	0.26	0.06 to 1.04	0.058
60–69	0.60	0.27 to 1.34	0.213	0.21	0.05 to 0.83	0.026
70–79	0.45	0.20 to 0.99	0.048	0.17	0.04 to 0.68	0.012
80+	0.46	0.21 to 1.03	0.060	0.18	0.05 to 0.73	0.016
Charlson Comorbidity Index
0	Ref			Ref
1	1.69	1.55 to 1.84	<0.001	1.63	1.49 to 1.79	<0.001
2	2.25	2.02 to 2.50	<0.001	1.76	1.56 to 1.98	<0.001
3+	3.01	2.66 to 3.41	<0.001	2.88	2.51 to 3.29	<0.001
Year (first surgery date)
2005	Ref			Ref
2006	0.98	0.89 to 1.07	0.648	0.92	0.83 to 1.01	0.085
2007	0.92	0.83 to 1.01	0.066	0.89	0.81 to 0.99	0.026
2008	0.96	0.86 to 1.06	0.378	0.86	0.77 to 0.96	0.009
2009	0.88	0.79 to 0.98	0.020	0.94	0.84 to 1.06	0.302
2010	0.81	0.71 to 0.91	<0.001	0.74	0.65 to 0.85	<0.001
2011	0.75	0.66 to 0.86	<0.001	0.76	0.66 to 0.88	<0.001
2012	0.69	0.60 to 0.81	<0.001	0.52	0.43 to 0.62	<0.001
2013	0.56	0.46 to 0.67	<0.001	0.47	0.37 to 0.59	<0.001
2014	0.56	0.45 to 0.70	<0.001	0.46	0.35 to 0.60	<0.001
Health network
Northern	Ref			Ref
Mid Central	1.08	1.00 to 1.18	0.065	1.10	1.01 to 1.21	0.032
Midland	1.07	0.99 to 1.16	0.095	1.16	1.06 to 1.26	0.001
Southern	1.04	0.96 to 1.13	0.298	1.12	1.03 to 1.22	0.008
Number of same type of surgeries in 2005–2017
One	Ref			Ref
Two	0.53	0.48 to 0.58	<0.001	0.56	0.51 to 0.61	<0.001

Ref, reference.