Trends in infant mortality and stillbirth rates in Scotland by socio-economic position, 2000–2018: a longitudinal ecological study

Table 4 Predicted incidence rate ratios (IRR) of infant mortality events obtained from negative binomial regression modelling using NS-SEC

	Model explanatory variables
	Year	NS-SEC	Infant sex	Maternal age
Reference category	2000	Class 1 (least disadvantaged)	Female	25–34 years
IRR for	Unit change	Unit change	Male	< 25 years	≥ 35 years
Infant mortality	0.97 * (0.96–0.97)	1.15 * (1.13–1.17)	1.22 * (1.15–1.30)	1.10 (1.01–1.18)	1.17 * (1.08–1.27)
Neonatal mortality^a	0.97 * (0.96–0.97)	1.12 * (1.10–1.14)	1.21 * (1.12–1.30)
Post-neonatal mortality^a	0.97 * (0.96–0.98)	1.22 * (1.19–1.26)	1.26 * (1.13–1.41)
Stillbirths	0.98 * (0.97–0.98)	1.15 * (1.14–1.18)	1.00 (0.94–1.05)	0.96 (0.90–1.04)	1.40 * (1.30–1.51)
Extended perinatal mortality	0.97 * (0.97–0.98)	1.15 * (1.13–1.16)	1.07 * (1.02–1.12)	0.99 (0.93–1.05)	1.32 * (1.25–1.41)

* p-value < 0.001
^a Note for neonatal mortality BIC for the model with and without adjustment for maternal age was 2651 and 2650, respectively, therefore adjustment for maternal age not included in the model. Similarly, for post-neonatal mortality, BIC for the model with and without adjustment for maternal age was 2137 and 2134, respectively, therefore adjustment for maternal age not included in the model

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