The Human Development Index (HDI) - UNDP
The United Nations Development Program (UNDP) gives the following definition:
"The HDI – human development index – is a summary composite index that measures a country's average achievements in three basic aspects of human development: longevity, knowledge, and a decent standard of living. Longevity is measured by life expectancy at birth; knowledge is measured by a combination of the adult literacy rate and the combined primary, secondary, and tertiary gross enrolment ratio; and standard of living by GDP per capita (PPP US$)"
It is therefore an alternative way to measure how developed is a country.
Isn't the "Human Development level" simply caused by the population's income?
Isn't the "Real" GDP per capita (Purchasing Power per capita) enough to measure this development level?
If it was true, both longevity and knowledge would depend on income.
For example, any poor country's population would always have low life expectancy at birth, low literacy rate and low enrolment ratios. Similarly, any rich country's population would always enjoy a long life and would be well-educated.
When checking the UNDP's data, any researcher can find out - not surprisingly - that shuch a positive correlation between income and either longevity or knowledge does exist. This correlation may involve a "cause-effect" relationship (knowledge makes you rich... being rich allows you to afford knowledge) but that's not the point. These correlations are not that perfect. There are indeed some rich (poor) countries with relatively low (high) achievements in terms of life expectancy and/or education statistics.
Let's just name a few of them (among the 20 most populous countries in the world: China, India, USA, Indonesia, Brazil, Pakistan, Bengladesh, Nigeria, Russia, Japan, Mexico, Philippines, Germany, Vietnam, Ethiopia, Turkey, Egypt, Iran, Thailand, France).
A typical rich country with relatively low achievements in terms of life expectancy is the USA. Even though its population benefits from the highest purchasing power in the world, life expectancy is only 77 years. That's well below Japan (81.5 years) and still below Germany (78.2 years) and France (78.8 years).
What about poor countries with relatively high life expectancy? Well, ironically, communist Vietnam is the best example!
Even though the Vietnamese population remains poor, its life expectancy is 69 years old. Does it look like a "short" life to you? Then, consider the stats from richer countries: Russia (66.7 years) or Brazil (68 years).
Education achievements can also be relatively disappointing for some rich countries. Japan's population shows a surprising picture. Enrollment ratios (for primary, secondary and tertiary schools) are only 84%. That's well below the stats in the USA (92%), France (91%) or Germany (88%)
Is there any example of a poor country enjoying high education achievements? Yes... Vietnam. Adult Literacy rate is 90%. That's much better than richer countries such as: Turkey (86.5%) or Iran (77.1%). However, the Vietnamese enrollment ratio is only 64%. It's roughly similar to other poor countries.