Do Gini index and PISA maths go together across countries?

Across 79 countries the link before adjusting for anything is r = -0.53, on a scale from -1 (opposite) to +1 (in step). A version that uses only each country's rank gives -0.54.

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

Comparing each country only with itself across 2003-2022, and setting aside what happened worldwide in each year, the link is -0.078 (42 countries, 266 country-years). Using year-to-year changes, it is —.

Does Gini index cause PISA maths?

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.

Gini index vs. PISA maths

Fades after adjusting for income

Across 79 countries, Gini index and PISA maths rise and fall together at r = -0.53 (on a scale from −1 to +1, where 0 means no link). Comparing only countries with similar income (GDP per person) leaves r = -0.43, which could easily be chance (q = 0.27, allowing for the many pairs tested, and allowing for countries in the same region being alike). Caution: much weaker within regions than across them (largely a between-region difference).

Comparing countries across the middle half of pisa maths, 387 to 478 PISA points, gini index is better by 5.84 points at the top of that range than the bottom. Comparing only countries with similar national income, the gap is 6.84 points.

Link before adjusting (r)-0.531p = 4.7e-7 · 79 countries

After adjusting for national income-0.430p = 8.4e-5 · likely range [-0.60, -0.23]

p, allowing for regions0.007standard error 0.084 · 5 regions

Check for luck (q)0.273across 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.

Gini index · index (0-100)link with income -0.34 · moderate

PISA maths · PISA pointslink with income +0.79 · high

“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	-0.531	4.7e-7	79
By rank (Spearman), not adjusted	-0.538	3.2e-7	79
Standard (Pearson), adjusted for national income	-0.430	8.4e-5	79
By rank (Spearman), adjusted for national income	-0.371	0.001	79

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 79 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: +0.101 (a minus sign means it grew).

How solid is it?

Leaving out one country at a time, r ranges from -0.457 (without DZA) to -0.378 (without PAN). 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: PAN (+0.053).

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
Europe & Central Asia	44	-0.26
Latin America & Caribbean	14	-0.08

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	27	-0.35
Middle third	26	-0.62
Richest third	26	-0.07

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	54	-0.59
Muslims	16	+0.30

By last european coloniser

	n	r
Spain	14	-0.11

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 = -0.440 after dropping 1 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 20years. So a link here can’t come from anything about a country that stays the same, such as its history, geography, institutions or culture.

Within countries over time, there is no link that is clearly more than chance (r = -0.078, comparing each country only with itself over the years, and each year only with the same year elsewhere). Whatever the cross-country picture shows, countries whose gini index moved did not tend to see their pisa maths move with it.

Across countries (adjusted)-0.430for comparison

Within countries-0.020each country vs itself

…and vs the same year elsewhere-0.078q = 0.632 · 42 countries

Year-on-year changes—q = —

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.

266 country-years (one country in one year), 42 countries, 2003–2022, about 6 years each on average. Share of the variation that happens within countries over time: 5% for Gini index, 6% for PISA maths. 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): -0.078. 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.

This curve peaks at the edge of the window (lag +6), so it is still drifting where the search stops. That pattern usually reflects a slow trend left over in the data, not a link with real timing. The peak value should not be read as the “true” link at the right lag.

The data

	index (0-100)	PISA points	Years
Colombia COL	54.4	383	2024, 2022
Brazil BRA	50.3	379	2024, 2022
Panama PAN	49.7	357	2024, 2022
Costa Rica CRI	45.5	385	2025, 2022
Guatemala GTM	45.2	344	2023, 2022
Paraguay PRY	44.2	338	2024, 2022
Turkiye TUR	43.7	453	2023, 2022
Chile CHL	43	412	2024, 2022
Mexico MEX	42.6	395	2024, 2022
Argentina ARG	42.4	378	2024, 2022
United States USA	41.8	465	2024, 2022
Malaysia MYS	40.7	409	2021, 2022
Peru PER	40.1	391	2024, 2022
Uruguay URY	40	409	2024, 2022
Jamaica JAM	39.9	377	2021, 2022

World Bank, World Development Indicators
OECD databases as named on each indicator: PISA, Social Expenditure Database (SOCX), Income Distribution Database, Development Assistance Committee statistics, Family Database, Government at a Glance, Corporate Tax Statistics, employment and environment statistics

Sources

Gini index

World Bank · CC BY 4.0 · updated quarterly

Sparse and uneven: most countries report only every few years, and coverage is thinnest where inequality is highest. Be wary of comparisons that match Gini with other measures year by year.

PISA maths

PISA mean mathematics score

OECD · via Our World in Data · CC BY 4.0 (OECD terms and conditions) · updated annual, except the snapshots noted per indicator

The average score of 15-year-olds on the same test in every country taking part. It is scaled so the OECD average in the starting year was 500, with a standard deviation (a typical gap between students) of 100. Held every three years. The 2021 round was held in 2022, and the OECD says it can still be compared with earlier rounds despite the pandemic. The three subjects are treated as measuring the same thing. Their links with each other are above 0.95, and that close match is a fact about the test, not about schooling.

How this was computed

Data used: most recent value in 2010-2025; values come from 2010–2025. 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 5 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 Gini index and PISA maths

This page shows that two measures go together. It does not show that Gini index changes PISA maths, or the reverse. These figures also describe countries, not individual people. See the ecological fallacy.