Across 180 countries, Fertility rate and Gender Development Index rise and fall together at r = -0.67 (on a scale from −1 to +1, where 0 means no link). Comparing only countries with similar income (GDP per person) shrinks it to -0.34, which could easily be chance (q = 0.22, 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: direction is not consistent across regions.
Comparing countries across the middle half of gender development index, 0.932 to 0.993 ratio of women's HDI to men's, fertility rate is 0.839 births per woman lower at the top of that range than the bottom. Comparing only countries with similar national income, the gap is 0.311 births per woman.
Link before adjusting (r)-0.673p = 4.5e-25 · 180 countries
After adjusting for national income-0.338p = 3.6e-6 · likely range [-0.46, -0.20]
p, allowing for regions0.001standard error 0.057 · 7 regions
Check for luck (q)0.223across 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.
Fertility rate · births per womanlink with income -0.81 · proxy
Gender Development Index · ratio of women's HDI to men'slink with income +0.65 · high
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
-0.673
4.5e-25
180
By rank (Spearman), not adjusted
-0.634
1.3e-21
180
Standard (Pearson), adjusted for national income
-0.338
3.6e-6
180
By rank (Spearman), adjusted for national income
-0.219
0.003
180
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 180 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: +0.334 (a minus sign means it grew).
How solid is it?
Leaving out one country at a time, r ranges from -0.365 (without SYR) to -0.310 (without TCD). 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: TCD (+0.028).
Fragile: this link may not hold up.
direction is not consistent across regions
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
30
+0.07
Europe & Central Asia
48
-0.33
Latin America & Caribbean
28
-0.27
Middle East, North Africa, Afghanistan & Pakistan
22
-0.34
Sub-Saharan Africa
44
-0.54
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
60
-0.36
Middle third
60
-0.18
Richest third
60
-0.03
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
105
-0.46
Muslims
48
-0.18
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
-0.28
Never a European colony
20
-0.22
Spain
19
+0.13
United Kingdom
60
-0.35
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 = -0.258 after dropping 13 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 34years. 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 = -0.389). It holds even when looking only at changes from one year to the next (r = -0.052). 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)-0.338for comparison
Within countries-0.635each country vs itself
…and vs the same year elsewhere-0.389q = 0.000 · 183 countries
Year-on-year changes-0.052q = 0.041
Read with care.
Almost all of the second indicator's variation is between countries, 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.
The association is much weaker in year-on-year changes than in levels, which points to shared country-specific trends.
4,929 country-years (one country in one year), 183 countries, 1990–2023, about 27 years each on average. Share of the variation that happens within countries over time: 11% for Fertility rate, 9% for Gender Development Index. 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): -0.389. 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
births per woman
ratio of women's HDI to men's
Years
Chad TCD
6.03
0.787
2024, 2023
Somalia, Fed. Rep. SOM
6.01
0.793
2024, 2023
Congo, Dem. Rep. COD
5.98
0.886
2024, 2023
Niger NER
5.93
0.855
2024, 2023
Mali MLI
5.51
0.812
2024, 2023
Angola AGO
5.05
0.906
2024, 2023
Burundi BDI
4.79
0.932
2024, 2023
Afghanistan AFG
4.76
0.66
2024, 2023
Mozambique MOZ
4.69
0.92
2024, 2023
Mauritania MRT
4.63
0.886
2024, 2023
Tanzania TZA
4.54
0.951
2024, 2023
Benin BEN
4.48
0.866
2024, 2023
Nigeria NGA
4.38
0.892
2024, 2023
Sudan SDN
4.26
0.813
2024, 2023
Cameroon CMR
4.26
0.898
2024, 2023
World Bank, World Development Indicators United Nations Development Programme, Human Development Report 2025
United Nations Development Programme, Human Development Report Office · via Our World in Data · CC BY 3.0 IGO · updated annual
The HDI worked out for women divided by the HDI worked out for men. It is above 1 where women score higher, as they do in several countries on health. So no "better" direction is set: equality is the aim, and equality is the middle of the scale, not one end of it.
How this was computed
Data used: most recent value in 2010-2025; values come from 2023–2024. 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 Fertility rate and Gender Development Index
This page shows that two measures go together. It does not show that Fertility rate changes Gender Development Index, or the reverse. These figures also describe countries, not individual people. See the ecological fallacy.
More links with Fertility rate or Gender Development Index