The Socio-demographic Index (SDI) is a composite metric developed by the Global Burden of Disease (GBD) Study to quantify a region or country's level of socio-demographic development.
Components
SDI is calculated as the geometric mean of three indicators:
Income per capita (lag-distributed)
Average educational attainment (years of schooling among individuals aged 15+)
Total fertility rate (TFR) among women under age 25
Scale and Interpretation
Ranges from 0 (lowest development) to 1 (highest development)
Enables categorization of countries/regions into:
High SDI
High–middle SDI
Middle SDI
Low–middle SDI
Low SDI
Purpose
To analyze how disease burden varies by socio-demographic status
To provide a contextual framework for interpreting health outcomes and risk factor exposure
To support comparative modeling across countries with different development levels
Applications
Used extensively in GBD estimates of:
Mortality
Disability-Adjusted Life Years (DALYs)
Risk factor attribution
Facilitates longitudinal and cross-country comparisons
Supports projections of future health burden
Example
Regions with low SDI often have a higher burden of infectious diseases and maternal mortality.
Regions with high SDI have a higher burden of non-communicable diseases (e.g., stroke, ICH), often with different risk factor profiles (e.g., aging, lifestyle, pollution).