placestats

Fertility rate vs. Median age

Holds up after adjusting for income

Across 199 countries, Fertility rate and Median age rise and fall together at r = -0.87 (on a scale from −1 to +1, where 0 means no link). Comparing only countries with similar income (GDP per person) shrinks it to -0.57 (q = 0.032, allowing for the many pairs tested). Much of the first figure is that both measures rise with national income, but a moderate negative link remains.

Comparing countries across the middle half of median age, 21.5 to 38.4 years, fertility rate is 1.89 births per woman lower at the top of that range than the bottom. Comparing only countries with similar national income, the gap is 1.35 births per woman.

Link before adjusting (r)-0.874p = 1.4e-63 · 199 countries
After adjusting for national income-0.573p = 1.1e-18 · likely range [-0.66, -0.47]
p, allowing for regions0.003standard error 0.118 · 7 regions
Check for luck (q)0.032across 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
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

Fertility rate · births per woman →Median age · years →0.5826.0314.349Aruba: 1.61 births per woman, 41 yearsAfghanistan: 4.76 births per woman, 16.9 yearsAngola: 5.05 births per woman, 16.5 yearsAlbania: 1.34 births per woman, 36.3 yearsAndorra: 1.09 births per woman, 43.2 yearsUnited Arab Emirates: 1.21 births per woman, 31.2 yearsArgentina: 1.5 births per woman, 32.1 yearsArmenia: 1.7 births per woman, 35.8 yearsAntigua and Barbuda: 1.58 births per woman, 35.5 yearsAustralia: 1.48 births per woman, 37.8 yearsAustria: 1.31 births per woman, 43.1 yearsAzerbaijan: 1.43 births per woman, 32.6 yearsBurundi: 4.79 births per woman, 15.9 yearsBelgium: 1.44 births per woman, 41.4 yearsBenin: 4.48 births per woman, 17.8 yearsBurkina Faso: 4.11 births per woman, 17.3 yearsBangladesh: 2.14 births per woman, 25.3 yearsBulgaria: 1.72 births per woman, 44.3 yearsBahrain: 1.8 births per woman, 32.9 yearsBahamas, The: 1.37 births per woman, 34.6 yearsBosnia and Herzegovina: 1.49 births per woman, 44.9 yearsBelarus: 1.22 births per woman, 40.5 yearsBelize: 2.02 births per woman, 25.9 yearsBermuda: 1.41 births per woman, 45.1 yearsBolivia: 2.52 births per woman, 24.7 yearsBrazil: 1.61 births per woman, 33.9 yearsBarbados: 1.71 births per woman, 38.9 yearsBrunei Darussalam: 1.73 births per woman, 31.8 yearsBhutan: 1.45 births per woman, 29.4 yearsBotswana: 2.7 births per woman, 22.9 yearsCentral African Republic: 5.95 births per woman, 14.3 yearsCanada: 1.25 births per woman, 40.3 yearsSwitzerland: 1.29 births per woman, 42.3 yearsChile: 1.14 births per woman, 36 yearsChina: 1.01 births per woman, 39.1 yearsCote d'Ivoire: 4.23 births per woman, 18.1 yearsCameroon: 4.26 births per woman, 17.8 yearsCongo, Dem. Rep.: 5.98 births per woman, 15.8 yearsCongo, Rep.: 4.11 births per woman, 18.3 yearsColombia: 1.63 births per woman, 31.6 yearsComoros: 3.82 births per woman, 20.3 yearsCabo Verde: 1.51 births per woman, 27.9 yearsCosta Rica: 1.32 births per woman, 34.1 yearsCuracao: 1.4 births per woman, 38.2 yearsCayman Islands: 1.52 births per woman, 37.9 yearsCyprus: 1.38 births per woman, 37.8 yearsCzechia: 1.36 births per woman, 42.7 yearsGermany: 1.36 births per woman, 45.1 yearsDjibouti: 2.62 births per woman, 24.4 yearsDominica: 1.48 births per woman, 35.6 yearsDenmark: 1.47 births per woman, 41.2 yearsDominican Republic: 2.22 births per woman, 27.7 yearsAlgeria: 2.72 births per woman, 28.2 yearsEcuador: 1.81 births per woman, 28.4 yearsEgypt, Arab Rep.: 2.73 births per woman, 24 yearsSpain: 1.1 births per woman, 44.9 yearsEstonia: 1.18 births per woman, 41.9 yearsEthiopia: 3.91 births per woman, 18.7 yearsFinland: 1.25 births per woman, 42.8 yearsFiji: 2.27 births per woman, 27.7 yearsFrance: 1.61 births per woman, 41.8 yearsFaroe Islands: 1.91 births per woman, 37.3 yearsMicronesia, Fed. Sts.: 2.74 births per woman, 22.9 yearsGabon: 3.59 births per woman, 21.5 yearsUnited Kingdom: 1.55 births per woman, 39.8 yearsGeorgia: 1.8 births per woman, 36.8 yearsGhana: 3.34 births per woman, 20.9 yearsGuinea: 4.13 births per woman, 18 yearsGambia, The: 3.91 births per woman, 18.2 yearsGuinea-Bissau: 3.76 births per woman, 18.9 yearsEquatorial Guinea: 4.12 births per woman, 21 yearsGreece: 1.24 births per woman, 45.7 yearsGrenada: 1.47 births per woman, 33.4 yearsGreenland: 1.71 births per woman, 34.2 yearsGuatemala: 2.29 births per woman, 22.6 yearsGuyana: 2.4 births per woman, 25.6 yearsHong Kong SAR, China: 0.841 births per woman, 46.2 yearsHonduras: 2.48 births per woman, 23.5 yearsCroatia: 1.46 births per woman, 44.8 yearsHaiti: 2.63 births per woman, 23.5 yearsHungary: 1.41 births per woman, 43.3 yearsIndonesia: 2.12 births per woman, 29.8 yearsIndia: 1.96 births per woman, 28.1 yearsIreland: 1.47 births per woman, 38.4 yearsIran, Islamic Rep.: 1.68 births per woman, 32.9 yearsIraq: 3.22 births per woman, 20.3 yearsIceland: 1.56 births per woman, 35.8 yearsIsrael: 2.87 births per woman, 29.1 yearsItaly: 1.18 births per woman, 47.5 yearsJamaica: 1.35 births per woman, 31.7 yearsJordan: 2.6 births per woman, 24.3 yearsJapan: 1.15 births per woman, 49 yearsKazakhstan: 2.98 births per woman, 29.5 yearsKenya: 3.17 births per woman, 19.5 yearsKyrgyz Republic: 2.6 births per woman, 25.1 yearsCambodia: 2.55 births per woman, 25.8 yearsKiribati: 3.12 births per woman, 22.7 yearsSt. Kitts and Nevis: 1.53 births per woman, 35.3 yearsKorea, Rep.: 0.748 births per woman, 44.5 yearsKuwait: 1.56 births per woman, 34.5 yearsLao PDR: 2.4 births per woman, 24.3 yearsLebanon: 2.23 births per woman, 28.3 yearsLiberia: 3.86 births per woman, 18.4 yearsLibya: 2.3 births per woman, 27.2 yearsSt. Lucia: 1.39 births per woman, 33.7 yearsSri Lanka: 1.95 births per woman, 32.8 yearsLesotho: 2.66 births per woman, 21.4 yearsLithuania: 1.11 births per woman, 42.1 yearsLuxembourg: 1.25 births per woman, 38.9 yearsLatvia: 1.24 births per woman, 43.1 yearsMacao SAR, China: 0.582 births per woman, 38.3 yearsMorocco: 2.21 births per woman, 29.2 yearsMoldova: 1.73 births per woman, 37.8 yearsMadagascar: 3.91 births per woman, 18.9 yearsMaldives: 1.56 births per woman, 31.1 yearsMexico: 1.89 births per woman, 28.9 yearsMarshall Islands: 2.86 births per woman, 20.7 yearsNorth Macedonia: 1.4 births per woman, 40.3 yearsMali: 5.51 births per woman, 15.5 yearsMalta: 1.01 births per woman, 40.3 yearsMyanmar: 2.1 births per woman, 29.5 yearsMontenegro: 1.8 births per woman, 39.3 yearsMongolia: 2.5 births per woman, 26.8 yearsMozambique: 4.69 births per woman, 16.3 yearsMauritania: 4.63 births per woman, 17.1 yearsMauritius: 1.44 births per woman, 36.9 yearsMalawi: 3.59 births per woman, 17.6 yearsMalaysia: 1.54 births per woman, 30.1 yearsNamibia: 3.21 births per woman, 21 yearsNiger: 5.93 births per woman, 15.3 yearsNigeria: 4.38 births per woman, 17.8 yearsNicaragua: 2.21 births per woman, 25.3 yearsNetherlands: 1.43 births per woman, 41.4 yearsNorway: 1.45 births per woman, 39.5 yearsNepal: 1.96 births per woman, 24.7 yearsNaoero: 3.29 births per woman, 20.4 yearsNew Zealand: 1.57 births per woman, 37.3 yearsOman: 2.51 births per woman, 29.3 yearsPakistan: 3.55 births per woman, 20.3 yearsPanama: 2.11 births per woman, 29.6 yearsPeru: 1.97 births per woman, 29.5 yearsPhilippines: 1.89 births per woman, 25.3 yearsPalau: 1.88 births per woman, 37.8 yearsPapua New Guinea: 3.07 births per woman, 22.3 yearsPoland: 1.14 births per woman, 41.3 yearsPuerto Rico (US): 0.92 births per woman, 45.3 yearsPortugal: 1.41 births per woman, 46.2 yearsParaguay: 2.42 births per woman, 26.3 yearsWest Bank and Gaza: 3.25 births per woman, 19.8 yearsQatar: 1.72 births per woman, 33.2 yearsRomania: 1.39 births per woman, 42.6 yearsRussian Federation: 1.42 births per woman, 39.5 yearsRwanda: 3.65 births per woman, 19.4 yearsSaudi Arabia: 2.31 births per woman, 29.2 yearsSudan: 4.26 births per woman, 18.3 yearsSenegal: 3.77 births per woman, 19.1 yearsSingapore: 0.97 births per woman, 35.1 yearsSolomon Islands: 3.51 births per woman, 20.3 yearsSierra Leone: 3.7 births per woman, 19.3 yearsEl Salvador: 1.77 births per woman, 27 yearsSan Marino: 1.16 births per woman, 47.4 yearsSomalia, Fed. Rep.: 6.01 births per woman, 15.4 yearsSerbia: 1.64 births per woman, 43.9 yearsSao Tome and Principe: 3.6 births per woman, 19.1 yearsSuriname: 2.23 births per woman, 28.1 yearsSlovak Republic: 1.46 births per woman, 41.3 yearsSlovenia: 1.52 births per woman, 43.9 yearsSweden: 1.43 births per woman, 39.9 yearsEswatini: 2.72 births per woman, 22 yearsSint Maarten (Dutch part): 1.44 births per woman, 41.6 yearsSeychelles: 1.85 births per woman, 33.7 yearsSyrian Arab Republic: 2.7 births per woman, 22.2 yearsTurks and Caicos Islands: 1.45 births per woman, 38.3 yearsChad: 6.03 births per woman, 15.4 yearsTogo: 4.12 births per woman, 18.1 yearsThailand: 1.2 births per woman, 39.7 yearsTajikistan: 3.04 births per woman, 21.9 yearsTurkmenistan: 2.66 births per woman, 26.2 yearsTimor-Leste: 2.63 births per woman, 21 yearsTonga: 3.1 births per woman, 20.7 yearsTrinidad and Tobago: 1.54 births per woman, 36.7 yearsTunisia: 1.82 births per woman, 32.1 yearsTurkiye: 1.48 births per woman, 32.5 yearsTuvalu: 3.17 births per woman, 24.3 yearsTanzania: 4.54 births per woman, 17.2 yearsUganda: 4.17 births per woman, 16.5 yearsUkraine: 0.988 births per woman, 42 yearsUruguay: 1.4 births per woman, 35.8 yearsUnited States: 1.63 births per woman, 38 yearsUzbekistan: 3.49 births per woman, 26.9 yearsSt. Vincent and the Grenadines: 1.76 births per woman, 33.9 yearsVirgin Islands (U.S.): 1.97 births per woman, 44.7 yearsViet Nam: 1.9 births per woman, 32.4 yearsVanuatu: 3.57 births per woman, 20.1 yearsSamoa: 3.8 births per woman, 19.9 yearsKosovo: 1.54 births per woman, 31.4 yearsSouth Africa: 2.21 births per woman, 28.2 yearsZambia: 4.04 births per woman, 17.5 yearsZimbabwe: 3.67 births per woman, 17.8 yearsCAFCODCPVHKGJPNKORNPLPHLSOMTCD

best-fit line line after adjusting

Four ways to measure the link

MethodrpCountries
Standard (Pearson), not adjusted-0.8741.4e-63199
By rank (Spearman), not adjusted-0.9171.9e-80199
Standard (Pearson), adjusted for national income-0.5731.1e-18199
By rank (Spearman), adjusted for national income-0.7331.3e-34199

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 199 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: +0.300 (a minus sign means it grew).

How solid is it?

Leaving out one country at a time, r ranges from -0.587 (without SOM) to -0.560 (without GUY). 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: GUY (+0.014).

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.

nr
East Asia & Pacific31-0.70
Europe & Central Asia53-0.69
Latin America & Caribbean38-0.68
Middle East, North Africa, Afghanistan & Pakistan22-0.78
Sub-Saharan Africa46-0.71

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.

nr
Poorest third67-0.84
Middle third66-0.69
Richest third66-0.68

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.

nr
Christians112-0.56
Muslims50-0.68

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.

nr
France25-0.83
Never a European colony21-0.72
Spain20-0.79
United Kingdom63-0.74

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 = -0.641 after dropping 5 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.

Loading…

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 = +0.201). It holds even when looking only at changes from one year to the next (r = +0.090). 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)-0.573for comparison
Within countries-0.542each country vs itself
…and vs the same year elsewhere+0.201q = 0.001 · 216 countries
Year-on-year changes+0.090q = 9.0e-5
The direction flips. Comparing each country only with itself gives -0.54. Also taking out what happened to the whole world each year gives +0.20. So the first figure was picking up a trend both measures share with worldwide progress, not a link between them.
Read with care.
  • 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.

7,344 country-years (one country in one year), 216 countries, 1990–2023, about 34 years each on average. Share of the variation that happens within countries over time: 10% for Fertility rate, 12% 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

0.50−0.5-100+10years Median age trails Fertility rate →lag -10: r = 0.459 (n = 5,400)lag -9: r = 0.445 (n = 5,616)lag -8: r = 0.430 (n = 5,832)lag -7: r = 0.411 (n = 6,048)lag -6: r = 0.389 (n = 6,264)lag -5: r = 0.365 (n = 6,480)lag -4: r = 0.336 (n = 6,696)lag -3: r = 0.306 (n = 6,912)lag -2: r = 0.274 (n = 7,128)lag -1: r = 0.241 (n = 7,344)lag +0: r = 0.201 (n = 7,344)lag +1: r = 0.166 (n = 7,128)lag +2: r = 0.130 (n = 6,912)lag +3: r = 0.095 (n = 6,696)lag +4: r = 0.060 (n = 6,480)lag +5: r = 0.026 (n = 6,264)lag +6: r = -0.004 (n = 6,048)lag +7: r = -0.031 (n = 5,832)lag +8: r = -0.056 (n = 5,616)lag +9: r = -0.078 (n = 5,400)lag +10: r = -0.095 (n = 5,184)

Same year (lag 0): +0.201. 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 -10), 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


births per woman
years		Years
Chad TCD6.0315.42024, 2023
Somalia, Fed. Rep. SOM6.0115.42024, 2023
Congo, Dem. Rep. COD5.9815.82024, 2023
Central African Republic CAF5.9514.32024, 2023
Niger NER5.9315.32024, 2023
Mali MLI5.5115.52024, 2023
Angola AGO5.0516.52024, 2023
Burundi BDI4.7915.92024, 2023
Afghanistan AFG4.7616.92024, 2023
Mozambique MOZ4.6916.32024, 2023
Mauritania MRT4.6317.12024, 2023
Tanzania TZA4.5417.22024, 2023
Benin BEN4.4817.82024, 2023
Nigeria NGA4.3817.82024, 2023
Sudan SDN4.2618.32024, 2023

World Bank, World Development Indicators
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

Fertility rate

Fertility rate, total (births per woman)

World Bank · CC BY 4.0 · updated quarterly

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 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 Median age

This page shows that two measures go together. It does not show that Fertility rate changes Median age, or the reverse. These figures also describe countries, not individual people. See the ecological fallacy.

More links with Fertility rate or Median age