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Table 2 Main input parameters to the modelling: selected baseline and epidemiological parameters

From: The health gains and cost savings of dietary salt reduction interventions, with equity and age distributional aspects

Variable Sources and key details Key values and uncertainty
Baseline variables in 2011  
Sodium intake Source: New Zealand (NZ) nutrition survey data [60], with significant variation by sex, but not by ethnicity or age (for adults). No trend under business-as-usual (BAU) specified, given no notable trend since the 1980s [61]. Although these values are based on spot urine tests, such tests are a reasonable means for studying populations as per this systematic review [62]. The values are also similar to previous NZ studies which have used 24-h urine collections [63]. 4013 mg/d for men and 3115 mg/d for women (nil uncertainty; rather uncertainty around the intervention associated reduction was considered – see below)
Incidence, prevalence and case-fatality data for CHD and stroke Calculated using linked Health Tracker data, with coherency checks using DisMod II and smoothing with regression as required. Future annual percentage change (APC) in incidence and CFR were both set at -2.0 % each as per the NZBDS. See online reports for details [19, 32].
Morbidity (disability weights [DW]) From GBD2010 [25], with modification to NZ [20] and slight variation by age and ethnicity (see an online report [19] for details). DW for CHD = 0.081 (average) DW for stroke = 0.226 (average). Uncertainty: e.g., for non-Māori males, 95%CI: 0.05–0.11 for CHD and 0.11–0.23 for stroke. (For more details uncertainty see Nghiem et al [19]).
Baseline health system costs for CHD and stroke states, and non-diseased states Calculated from Health Tracker data by sex and age in 2011 for people: (a) without either CHD or stroke; (b) with CHD only, and excess to (a); (c) with stroke only, and excess to (a). (See an online report [19] for details). Examples for 60 year old women (gamma distribution with SD = 10 % of mean): (a) NZ$2381; (b) NZ$16,258 for the first year, NZ$5,395 for second and subsequent years; (c) NZ$20,553 and NZ$5991 for stroke.
Epidemiological associations  
Change in systolic blood pressure (sBP) (in mm Hg) for each 100 mmol/d change in sodium intake Derived from the regressions models developed by Law et al [35]. The small differences in BP by ethnic group did not justify separate modelling by ethnicity (higher in Māori by 3 mm Hg for systolic BP and 4 mm Hg for diastolic BP in both sexes compared to non-Māori [64]). Also of note is that no trend in BP into the future was considered given the unclear picture in NZ (of a downward trend in population BP levels from 1982 to 2002 and then an upward trend from then 2008/09) [64]. For men and women:
Age-group; sBP (mm Hg) change
30–39: 5.5
40–49: 6.6
50–59: 9.2
60–69: 10.3
Relationship between blood pressure and CVD risks We used the results of a meta-analysis of 61 prospective studies by Lewington et al [36]. These results were considered to be more generalisable to the general population than those from a meta-analysis by Law et al 2009 of 147 RCTs of blood pressure-lowering drugs [65]. The hazard ratio for a 20 mm Hg reduction in systolic BP ranged from 0.49 to 0.67 for CHD and from 0.38 to 0.67 for stroke (depending on age). For uncertainty: SD = +/- 10 % of the point estimate for each age group.