Sensitivity of Risk Factor Estimates to Variations in Key Parameter Values
Figures 5.9 to 5.11 examine the sensitivity of the burden of disease attributable to each of the 19 risk factors discussed in chapter 4 to key DALY discounting and age-weighting parameters for the world, for low-and-middle-income countries, and for high-income countries. The figures plot the attributable disease burden estimated by altering one key parameter against the baseline of DALYs(3,0) used in chapter 4. To allow comparability, all burdens attributable to risk factors are shown as a proportion of the total global or regional disease burden, which is itself estimated with the corresponding parameters.
Including age weighting, DALYs(3,1), increases the relative health consequences of risks that affect people in young and middle ages (alcohol use, illicit drug use, and unsafe sex) and lowers the relative contribution of those risks that result in death in older ages (high blood pressure, high cholesterol, low fruit and vegetable intake, overweight and obesity, physical inactivity, and smoking). In addition, the burden of disease attributable to childhood and maternal underweight increases as a proportion of the total global or regional burden of disease. This increase probably reflects a relative reduction in the total burden of those diseases that affect older adults, and hence a relative increase in the total burden of those diseases that affect young children. Because childhood and maternal underweight is a risk factor for this latter group of diseases, its attributable burden as a share of the total global or regional disease burden increases.
Removing discounting, DALYs(0,0), results in a large relative increase in the disease burden attributable to risk factors that affect young children, including childhood underweight; indoor smoke from household use of solid fuels; unsafe water, sanitation, and hygiene; vitamin A deficiency; and zinc deficiency. This is mirrored by a decrease in the disease burden attributable to the risk factors for diseases that affect adults, because the total burden of the chronic diseases affected by these risks is reduced. This effect is more noticeable in the low- and middle-income countries than in the high-income countries, where childhood mortality is low and the overall share of the disease burden is less sensitive to discounting.
Sensitivity to key DALY parameters differed in the low- and middle-income countries and the high-income countries. The burden of disease attributable to risk factors for chronic diseases in adults (high blood pressure, high cholesterol, low fruit and vegetable intake, overweight and obesity, physical inactivity, and smoking) was more sensitive to these parameters in low- and middle-income countries than in high-income countries because deaths attributable to these risks occurred at younger ages in the former. By contrast, the burden of disease attributable to alcohol was much more sensitive to age-weighting in the high-income countries because many of the hazards of this risk, especially those related to injuries and neuropsychiatric conditions, occur among younger adults in this group of countries.