Inequality-adjusted HDI vs. Median age
Fades after adjusting for income
Across 167 countries, Inequality-adjusted HDI and Median age rise and fall together at r = +0.90 (on a scale from −1 to +1, where 0 means no link). Comparing only countries with similar income (GDP per person) shrinks it to +0.46, which could easily be chance (q = 0.11, allowing for the many pairs tested, and allowing for countries in the same region being alike). So the first figure mostly shows richer countries differing from poorer ones, not a link between these two things. Caution: much weaker within regions than across them (largely a between-region difference).
Comparing countries across the middle half of median age, 20.4 to 38.9 years, inequality-adjusted hdi is better by 0.336 points at the top of that range than the bottom. Comparing only countries with similar national income, the gap is 0.127 points.
Link before adjusting (r)+0.896p = 4.7e-60 · 167 countries
After adjusting for national income+0.464p = 3.0e-10 · likely range [+0.34, +0.58]
p, allowing for regions0.009standard error 0.123 · 7 regions
Check for luck (q)0.107across 12,497 pairs
How to read these.r runs from −1 (one goes up as the other goes down) to +1 (they rise together), and 0 means no link. Adjusting for national income means comparing countries with the same GDP per person, so differences in wealth can’t explain the link. Income is used in percentage terms, since an extra $1,000 means more to a poor country than to a rich one. p is how likely a link this strong would be if there were really none. Below 0.05 means it is unlikely to be chance. Very small values are written in short form: 1.1e-32 means a decimal point followed by 31 zeros and then 11, so very close to zero. The likely range is where the true figure probably lies, and a range that crosses zero means the link could easily be chance. Countries in the same region tend to resemble each other, so the third figure allows for that, which gives a fairer p. The standard error is the typical size of the error in r. Finally, testing this many pairs means some will look strong by luck alone. A q below 0.05 means this link is unlikely to be one of those.
Inequality-adjusted HDI · index, 0 to 1link with income +0.94 · proxy
Median age · yearslink with income +0.86 · proxy
Both of these rise and fall closely with national income, so a strong link between them before adjusting was close to certain. Read the adjusted figure, not the first one.
“Link with income” is how closely each measure tracks GDP per person across countries, from −1 to +1.
Every country as a dot
best-fit line line after adjusting
Four ways to measure the link
| Method | r | p | Countries |
|---|---|---|---|
| Standard (Pearson), not adjusted | +0.896 | 4.7e-60 | 167 |
| By rank (Spearman), not adjusted | +0.895 | 9.6e-60 | 167 |
| Standard (Pearson), adjusted for national income | +0.464 | 3.0e-10 | 167 |
| By rank (Spearman), adjusted for national income | +0.397 | 1.2e-7 | 167 |
The rank version uses only each country’s place in line, from lowest to highest, so a few extreme countries count for less. The adjusted and unadjusted versions use the same 167 countries: those that report both measures and GDP per person. So the gap between them comes from the adjustment, not from a change in which countries are counted. Drop in the size of r after adjusting: +0.432 (a minus sign means it grew).
How solid is it?
Leaving out one country at a time, r ranges from +0.448 (without AGO) to +0.489 (without TON). The bar above shows that range on a scale from −1 to +1, with the solid line at the full result. The single country that moves r most: TON (+0.025).
Fragile: this link may not hold up.
- much weaker within regions than across them (largely a between-region difference)
Within each region
Countries are not separate, unrelated cases, and neighbors share a lot. A link that holds inside each region is far more believable than one that shows up only when comparing regions.
| n | r | ||
|---|---|---|---|
| East Asia & Pacific | 29 | +0.17 | |
| Europe & Central Asia | 47 | +0.13 | |
| Latin America & Caribbean | 22 | +0.12 | |
| Middle East, North Africa, Afghanistan & Pakistan | 16 | +0.05 | |
| Sub-Saharan Africa | 45 | +0.61 |
By income third
If the link shows up only in the richest third of countries, it is a feature of rich countries, not a general pattern.
| n | r | ||
|---|---|---|---|
| Poorest third | 56 | +0.39 | |
| Middle third | 55 | +0.45 | |
| Richest third | 56 | +0.52 |
By largest religious group
Countries grouped by a label they share, such as main religion, rather than by a number. Groups of fewer than twelve countries are not shown. These groups differ in income, region and history all at once. So a gap between them is a place to start asking questions, not an answer.
| n | r | ||
|---|---|---|---|
| Christians | 100 | +0.55 | |
| Muslims | 41 | +0.41 |
By last european coloniser
Countries grouped by a label they share, such as main religion, rather than by a number. Groups of fewer than twelve countries are not shown. These groups differ in income, region and history all at once. So a gap between them is a place to start asking questions, not an answer.
| n | r | ||
|---|---|---|---|
| France | 24 | +0.68 | |
| Never a European colony | 18 | +0.15 | |
| Spain | 18 | +0.51 | |
| United Kingdom | 51 | +0.26 |
Without outliers (countries far outside the middle half of countries on either measure, by more than one and a half times the width of that middle half): r = +0.464 after dropping 0 countries.
Two series, one country
Both measures over the years for one country you pick. The two charts are stacked so they share only the years along the bottom.
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Over time, within countries
Everything above compares countries with each other at one moment. This section compares each country only with itself over 14years. So a link here can’t come from anything about a country that stays the same, such as its history, geography, institutions or culture.
The link also shows up within countries over time (r = +0.210). It holds even when looking only at changes from one year to the next (r = +0.104). This is the strongest kind of evidence available here: it holds when each country is compared only with itself, and it is not just a product of shared trends.
Across countries (adjusted)+0.464for comparison
Within countries+0.728each country vs itself
…and vs the same year elsewhere+0.210q = 0.008 · 166 countries
Year-on-year changes+0.104q = 0.047
Read with care.
- Almost all of this indicator's variation is between countries, not within them, so the within-country estimate rests on a small part of the data.
- Much of the within-country association disappears once shared global year effects are removed, which points to a common worldwide trend rather than a country-level relationship.
2,131 country-years (one country in one year), 166 countries, 2010–2023, about 13 years each on average. Share of the variation that happens within countries over time: 1% for Inequality-adjusted HDI, 1% for Median age. The margins of error allow for each country appearing many times, and for each year’s value being close to the year before.
Year-to-year changes are a cautious test, not a final answer. Looking only at changes from one year to the next removes each country’s own trends. But it also makes measurement mistakes louder, which pulls the results toward zero. A near-zero result here is weak evidence of no link, not proof.
With one measure years behind the other
Same year (lag 0): +0.210. A peak away from zero does not show which comes first. These series change slowly — this year’s value is close to last year’s. That makes the curve smooth and nearly symmetric, whatever produced the data. Even a sharp peak at one lag (a gap of some years) would not prove that one measure changes the other.
The data
index, 0 to 1 | years | Years | |
|---|---|---|---|
| Iceland ISL | 0.923 | 35.8 | 2023 |
| Norway NOR | 0.909 | 39.5 | 2023 |
| Denmark DNK | 0.909 | 41.2 | 2023 |
| Switzerland CHE | 0.894 | 42.3 | 2023 |
| Netherlands NLD | 0.892 | 41.4 | 2023 |
| Finland FIN | 0.891 | 42.8 | 2023 |
| Belgium BEL | 0.891 | 41.4 | 2023 |
| Germany DEU | 0.89 | 45.1 | 2023 |
| Sweden SWE | 0.886 | 39.9 | 2023 |
| Ireland IRL | 0.886 | 38.4 | 2023 |
| Slovenia SVN | 0.885 | 43.9 | 2023 |
| Australia AUS | 0.873 | 37.8 | 2023 |
| United Kingdom GBR | 0.869 | 39.8 | 2023 |
| Czechia CZE | 0.867 | 42.7 | 2023 |
| Canada CAN | 0.867 | 40.3 | 2023 |
United Nations Development Programme, Human Development Report 2025
United Nations, Department of Economic and Social Affairs, Population Division: World Population Prospects 2024 and Estimates and Projections of Women of Reproductive Age Who Are Married or in a Union
Sources
Inequality-adjusted HDI
Inequality-adjusted Human Development Index
United Nations Development Programme, Human Development Report Office · via Our World in Data · CC BY 3.0 IGO · updated annual · comparable from 2010 only
The HDI marked down for how unequally each of its three parts is spread within the country. The gap between this and the HDI is what inequality costs, and that is the number worth reading. The level itself is the HDI again, with its parts flagged the same way.
Median age
Median age of the population
United Nations Department of Economic and Social Affairs, Population Division · via Our World in Data · CC BY 3.0 IGO · updated biennial
The age that splits a population in half: half are older and half are younger. The shares aged under 15 and over 65 are already on the site. All three are treated as measuring the same thing. They are readings of the same age pyramid, so they are bound to match, and their agreement is not a finding. No "better" direction is set.
How this was computed
Data used: most recent value in 2010-2025; values come from 2015–2023. To adjust for income, each measure is first predicted from GDP per person (in percentage terms, on a log scale) with a straight-line fit. Only what is left over is then compared. This is called a partial correlation. The line is drawn the standard way (ordinary least squares), which picks the line that comes closest to all the countries at once. The error margins allow for countries in the same region resembling each other, using 7 World Bank regions. The q-value corrects for testing all 12,497 pairs at once, using the Benjamini–Hochberg method. Underlying data last updated DYB 2024. How the country data works · explore Inequality-adjusted HDI and Median age
This page shows that two measures go together. It does not show that Inequality-adjusted HDI changes Median age, or the reverse. These figures also describe countries, not individual people. See the ecological fallacy.
More links with Inequality-adjusted HDI or Median age
- Median age vs Public social spending before +0.65 → after adjusting +0.59
- Informal employment vs Median age before -0.88 → after adjusting -0.51
- Inequality-adjusted HDI vs Redistribution before +0.75 → after adjusting +0.50
- Inequality-adjusted HDI vs Life expectancy before +0.90 → after adjusting +0.50
- Median age vs Population growth before -0.61 → after adjusting -0.47
- Inequality-adjusted HDI vs Under-5 mortality before -0.85 → after adjusting -0.47
- Inequality-adjusted HDI vs PISA maths before +0.84 → after adjusting +0.47
- Inequality-adjusted HDI vs Physicians before +0.85 → after adjusting +0.46