The Historical Index of Human Development (HIHD) provides a composite measure of development using metrics of life expectancy, literacy, educational enrolment and gross domestic product (GDP) per capita. The chart below shows the comparison of the HIHD with and without the inclusion of the GDP per capita metric. The Human Development Index (HDI) is a statistic composite index of life expectancy, education, and per capita income indicators, which are used to rank countries into four tiers of human development. A country scores a higher HDI when the lifespan is higher, the education level is higher, and the gross national income GNI (PPP) per capita is The Human Development Index (HDI) is a statistic composite index of life expectancy, education, and per capita income indicators, which are used to rank countries into four tiers of human development. A country scores a higher HDI when the lifespan is higher, the education level is higher, and the gross national income GNI (PPP) per capita is