Q.Explain the three dimensions used to construct the Human Development Index.

HDI rests on three dimensions: health, knowledge, and standard of living.

The Human Development Index is built on three dimensions, each converted into a dimension index using the formula

1. A long and healthy life — measured by life expectancy at birth, capturing the health dimension of development.
2. Knowledge — measured by a combination of mean years of schooling (for adults aged 25 and above) and expected years of schooling (for children entering school), capturing the education dimension.
3. A decent standard of living — measured by Gross National Income (GNI) per capita, in purchasing-power-parity (PPP) dollars, capturing the income dimension.

The overall HDI is then computed as the geometric mean of the three dimension indices, $HDI = \sqrt[3]{I_{health} \times I_{education} \times I_{income}}$, giving a single score between 0 and 1 that reflects health, education, and income together rather than income alone.

Naming only two of the three dimensions, or forgetting that the combination is a geometric mean rather than a simple average.