Why can HDI reveal more about development than GDP per capita?

The Human Development Index (HDI) can reveal more about development than GDP per capita because it includes health and education alongside income. Average production alone cannot tell us whether people live long lives or have opportunities to learn. However, HDI is still a summary measure, not a complete account of well-being.

GDP per capita is gross domestic product, the value of output produced within a country, divided by its population. International comparisons often use purchasing power parity (PPP) to allow for differences in what money can buy. HDI's income component uses GNI per capita, or gross national income per person, which concerns residents' income rather than domestic output. Its other components are life expectancy at birth, mean years of schooling among adults, and expected schooling years for children.

Compare these hypothetical countries. Their income and output values use the same PPP basis. For this example, we assume GDP and GNI per capita are equal.

GDP per capita alone places them level. Yet Alder's longer life expectancy and more years of schooling show advantages that the output comparison misses. These data do not by themselves prove which policies caused the difference.

HDI first converts health, education and income to comparable scores, called dimension indices. These are H, E and I below. It then takes their geometric mean: multiply the scores and take the cube root.

$$HDI=(H\times E\times I)^{1/3}.$$

Using the 2025 UNDP technical method, Alder has the following scores. The fixed benchmarks put the dimensions on comparable scales; they are not the lowest and highest values in this two-country example. The education score averages the two schooling scores. The income formula uses the natural logarithm, written ln.

$$H=\frac{78-20}{85-20}\approx0.8923,$$ $$E=\frac{12/15+16/18}{2}\approx0.8444,$$ $$I=\frac{\ln(20{,}000)-\ln(100)}{\ln(75{,}000)-\ln(100)}\approx0.8003.$$

Its illustrative HDI is about 0.845. Applying the same method to Birch gives about 0.668. These are calculated examples, not published country scores. Because the scores are multiplied rather than added, a strong income score cannot simply cancel out a very weak health or education score.

HDI also leaves questions unanswered. National averages can hide inequalities between regions or social groups. Years spent at school do not directly measure what pupils learned, and life expectancy does not describe every aspect of health. HDI also omits direct measures of political freedom and environmental sustainability. Choosing its components and their weights involves judgements about what matters.

Use GDP per capita to examine average economic output, then HDI and its separate components to look beyond output. You also need evidence about how gains are shared, and other social or environmental measures, before concluding that everyone benefits from development.

Try the question comparing single and composite indicators in the first Economics HL mock-exam set. Explain what health and education add to an income-only comparison, then identify what a combined score can still hide.