Do Inequality-adjusted HDI and Religiously unaffiliated go together across countries?

Across 162 countries the link before adjusting for anything is r = +0.51, on a scale from -1 (opposite) to +1 (in step). A version that uses only each country's rank gives +0.55.

Does the link hold within countries over time, not just across countries?

There are not enough years of data within countries to check this over time.

Does Inequality-adjusted HDI cause Religiously unaffiliated?

This analysis cannot answer that. It shows only that the two go together. A link between two country measures, adjusted or not, does not show that either one changes the other. Country figures also say nothing about individual people.

Inequality-adjusted HDI vs. Religiously unaffiliated

Fades after adjusting for income

A country is not a person. Countries where more people are counted as belonging to this group also tend to differ on the other measure, and that is all. It does not follow that the people in the group are the people with the different score. Making that leap is called the ecological fallacy: reading a pattern across places as a fact about individual people. It is the most common misuse of this kind of data. Religion also varies strongly with region, history and national income, so much of what looks religious here is really those. That is what the adjusted figures are for. The religion shares are estimates for two years only, and the survey questions are asked in rounds that can be ten years apart.

Across 162 countries, Inequality-adjusted HDI and Religiously unaffiliated rise and fall together at r = +0.51 (on a scale from −1 to +1, where 0 means no link). Comparing only countries with similar income (GDP per person) shrinks it to +0.18, which could easily be chance (q = 0.19, 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.

Comparing countries across the middle half of religiously unaffiliated, 0.395% to 15% of population, inequality-adjusted hdi is better by 0.088 points at the top of that range than the bottom. Comparing only countries with similar national income, the gap is 0.0125 points.

Link before adjusting (r)+0.510p = 4.2e-12 · 162 countries

After adjusting for national income+0.180p = 0.022 · likely range [+0.03, +0.33]

p, allowing for regions0.002standard error 0.035 · 7 regions

Check for luck (q)0.191across 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

Religiously unaffiliated · % of populationlink with income +0.51 · moderate

“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	+0.510	4.2e-12	162
By rank (Spearman), not adjusted	+0.551	2.9e-14	162
Standard (Pearson), adjusted for national income	+0.180	0.022	162
By rank (Spearman), adjusted for national income	+0.059	0.455	162

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 162 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: +0.330 (a minus sign means it grew).

How solid is it?

Leaving out one country at a time, r ranges from +0.165 (without CZE) to +0.207 (without CHN). 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: CHN (+0.026).

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	25	+0.31
Europe & Central Asia	46	+0.50
Latin America & Caribbean	22	+0.40
Middle East, North Africa, Afghanistan & Pakistan	16	-0.01
Sub-Saharan Africa	45	+0.07

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	54	-0.03
Middle third	54	-0.01
Richest third	54	+0.44

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	+0.14
Muslims	41	+0.00

By last european coloniser

	n	r
France	24	+0.48
Never a European colony	18	-0.12
Spain	18	+0.29
United Kingdom	49	+0.24

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 = +0.124 after dropping 15 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 0years. So a link here can’t come from anything about a country that stays the same, such as its history, geography, institutions or culture.

Not enough history inside each country to look at this over time. That needs countries measured for several years in a row, and at least one of these measures is measured too rarely.

The data

	index, 0 to 1	% of population	Years
Iceland ISL	0.923	19.8%	2023, 2020
Norway NOR	0.909	22.5%	2023, 2020
Denmark DNK	0.909	16.6%	2023, 2020
Switzerland CHE	0.894	30.8%	2023, 2020
Netherlands NLD	0.892	54.1%	2023, 2020
Finland FIN	0.891	25%	2023, 2020
Belgium BEL	0.891	39%	2023, 2020
Germany DEU	0.89	36.1%	2023, 2020
Sweden SWE	0.886	28.9%	2023, 2020
Ireland IRL	0.886	15.6%	2023, 2020
Slovenia SVN	0.885	32.3%	2023, 2020
Australia AUS	0.873	42.3%	2023, 2020
United Kingdom GBR	0.869	40.2%	2023, 2020
Czechia CZE	0.867	72.8%	2023, 2020
Canada CAN	0.867	34.6%	2023, 2020

United Nations Development Programme, Human Development Report 2025
Pew Research Center, Religious Composition by Country, 2010-2020. Pew Research Center bears no responsibility for the analyses or interpretations of the data presented here.
One of these measures is published under a licence that forbids changes. Values are shown exactly as published and must not be republished in a changed or rescaled form.

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.

Religiously unaffiliated

Share of the population religiously unaffiliated

Pew Research Center · via Our World in Data · Pew Research Center terms of use, excerpts with attribution · updated decennial · comparable from 2010 only

People who belong to no religion: atheists, agnostics and those who say "nothing in particular". Pew estimated it from censuses and surveys for 2010 and 2020. Belonging is a third thing, beside the attendance and importance measures already here. A country can be almost all affiliated and rarely attend, as much of Europe is. With only two years, nothing here shows a trend. 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 Religiously unaffiliated

This page shows that two measures go together. It does not show that Inequality-adjusted HDI changes Religiously unaffiliated, or the reverse. These figures also describe countries, not individual people. See the ecological fallacy.