GBD classifies risks in a hierarchy containing four levels. To increase accessibility and transparency of GBD 2021 estimates, we have prepared summaries for each risk factor at Level 2 through Level 4. A selection of these appear in the main text of the research article, and all are available online.
Level 1 risks are aggregates of environmental and occupational risks, behavioral risks, and metabolic risks. These aggregates are not presented in the summaries.
At Level 2, there are 20 risk categories, including air pollution, child and maternal malnutrition, and high body mass index.
Level 3 risks include more specific risks such as particulate matter pollution and child growth failure. In some cases, these Level 3 risks are the most detailed classification, while for others a more detailed category is specified at Level 4. Examples of Level 4 risks include household air pollution from solid fuels, and child stunting. The metabolic risks aggregate does not include any Level 3 or 4 risks.
Each two-page summary begins with a summary results statement, a definition of the risk, and a brief listing of modeling updates in GBD 2021 compared to previous GBD rounds.
Table 1 provides the total number of sources for exposure and relative risk used in GBD 2021 estimation for the risk.
Table 2 presents global numbers of attributable deaths, years of life lost (YLLs, estimated as death counts multiplied by remaining life expectancy from a standard life table), years lived with disability (YLDs, estimated as prevalent cases multiplied by a disability weight reflecting the severity of each disease outcome), and disability-adjusted life years (DALYs, the sum of YLLs and YLDs) for each risk for both sexes combined, males, and females in 2021. Age-standardized rates (age-specific rates adjusted to the GBD global standard population) are also provided, along with percentage change for each metric from 2010 to 2021. Dashes represent metrics for which estimates were not produced.
Table 3 provides rankings of deaths, YLLs, YLDs, and DALYs for the risk factor in 1990, 2010, and 2021.
Figure 1 displays the risk factor’s attributable global DALYs broken down by Level 2 causes. For risks with more than 10 Level 2 cause pairs, the 10 causes contributing the largest number of DALYs are shown.
Figure 2 disaggregates attributable global DALYs into YLLs and YLDs by age group and by sex.
Figure 3 illustrates the distribution of age-standardized all-cause summary exposure values (SEV, a measure of exposure to a risk factor normalized on a scale of 0 to 100 to make comparisons possible between dichotomous, polytomous, and continuous risks) by country or territory, and selected subnational locations.
Figure 4 presents the percentage change from 1990 to 2021 for all-cause age-standardized SEV by Socio-demographic Index (SDI, a summary measure of income per capita, fertility, and education ranging from the lowest sociodemographic status at zero to and the highest at 100).
For risks that do not produce a SEV as part of their modeling process, the population attributable fraction (PAF, i.e., the proportion of a disease that is estimated to be attributed to the risk factor given its exposure in a population and the relative risk of the outcome between those exposed and those exposed at the theoretical minimum risk level) is shown instead.
Where applicable, Figure 5 shows the proportion of the susceptible population that was exposed to each level of the risk factor in 2021. The susceptible population includes everyone in the age groups modeled for that risk.
Where applicable, Figure 6 displays the all-cause mortality relative risk for the risk factor within the population susceptible to that risk.
