A single measure that combines multiple individual indicators into one index to provide an overall assessment.
Single indicators each capture only one dimension, so on their own they can mislead.
Because development is multi-dimensional, economists use composite indicators, which combine several dimensions into one score.
The Human Development Index (HDI) is the most widely used.
Besides the HDI, three other composites are worth knowing.
Gender Inequality Index (GII): the loss in development from gender gaps in health, empowerment, and the labour market.
Inequality-adjusted HDI (IHDI): the HDI discounted for how unequally health, education, and income are spread.
Happy Planet Index (HPI): well-being and life expectancy set against a country's ecological footprint.
The Human Development Index
The HDI is the best-known composite, blending three dimensions.
A long and healthy life: measured by life expectancy at birth.
Knowledge: measured by mean and expected years of schooling.
A decent standard of living: measured by GNI per capita at PPP.
Each dimension is first turned into an index from 0 to 1.
The HDI is the geometric mean of the three, $HDI = \sqrt[3]{I_{health} \times I_{education} \times I_{income}}$, so a weak dimension drags the whole score down.
Countries score from 0 to 1 and fall into four bands.
Very high: 0.800 or above.
High: 0.700 to 0.799.
Medium: 0.550 to 0.699.
Low: below 0.550.
At the top, Switzerland and Norway score near 0.97; Niger, near 0.4, is among the lowest.
Its biggest blind spot is distribution: the same HDI can hide very different inequality.
It also ignores the environment, political freedom, and human rights.
So a high HDI can sit beside pollution or repression.
Even so, it is a strong first cut, best read alongside the IHDI and GII.
Case study
Equatorial Guinea earns rich-country income per head from oil, but weak health and education leave its HDI rank far below its GNI-per-capita rank.
That gap is exactly what the HDI is built to reveal: income alone does not decide development.
Active recall
Name the three dimensions of the HDI and the indicator used for each.
Why is the HDI a geometric mean rather than a simple average of the three indices?
Give two things the HDI still fails to capture, and name an indicator that addresses one of them.
Name one country whose GNI-per-capita rank sits well above its HDI rank, and explain why.
