Across 197 countries, Adolescent fertility and Basic sanitation rise and fall together at r = -0.81 (on a scale from −1 to +1, where 0 means no link). Comparing only countries with similar income (GDP per person) shrinks it to -0.53 (q = 0.021, 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. Caution: much weaker within regions than across them (largely a between-region difference).
Comparing countries across the middle half of basic sanitation, 71.2% to 99% of population, adolescent fertility is better by 32.9 births per 1,000 women aged 15-19 at the top of that range than the bottom. Comparing only countries with similar national income, the gap is 22.3 births per 1,000 women aged 15-19.
Link before adjusting (r)-0.809p = 8.6e-47 · 197 countries
After adjusting for national income-0.527p = 2.2e-15 · likely range [-0.62, -0.42]
p, allowing for regions0.002standard error 0.099 · 7 regions
Check for luck (q)0.021across 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.
Adolescent fertility · births per 1,000 women aged 15-19link with income -0.81 · proxy
Basic sanitation · % of populationlink with income +0.79 · 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
-0.809
8.6e-47
197
By rank (Spearman), not adjusted
-0.800
4.1e-45
197
Standard (Pearson), adjusted for national income
-0.527
2.2e-15
197
By rank (Spearman), adjusted for national income
-0.440
1.1e-10
197
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 197 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: +0.282 (a minus sign means it grew).
How solid is it?
Leaving out one country at a time, r ranges from -0.543 (without ETH) to -0.515 (without COG). 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: ETH (-0.017).
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
31
-0.12
Europe & Central Asia
52
-0.67
Latin America & Caribbean
37
+0.02
Middle East, North Africa, Afghanistan & Pakistan
22
-0.03
Sub-Saharan Africa
46
-0.40
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
66
-0.55
Middle third
65
-0.56
Richest third
66
-0.53
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
111
-0.40
Muslims
49
-0.73
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
25
-0.56
Never a European colony
21
-0.43
Spain
19
-0.63
United Kingdom
63
-0.49
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 = -0.525 after dropping 19 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 25years. 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 = -0.263). It holds even when looking only at changes from one year to the next (r = -0.150). 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)-0.527for comparison
Within countries-0.566each country vs itself
…and vs the same year elsewhere-0.263q = 0.008 · 214 countries
Year-on-year changes-0.150q = 0.002
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.
5,166 country-years (one country in one year), 214 countries, 2000–2024, about 24 years each on average. Share of the variation that happens within countries over time: 4% for Adolescent fertility, 5% for Basic sanitation. 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): -0.263. 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 1,000 women aged 15-19
% of population
Years
Central African Republic CAF
161
14%
2024
Equatorial Guinea GNQ
153
66.3%
2024, 2017
Mozambique MOZ
152
38.6%
2024
Niger NER
142
16.3%
2024
Angola AGO
139
50.3%
2024, 2022
Mali MLI
136
47.8%
2024
Chad TCD
132
13.1%
2024
Madagascar MDG
129
15.4%
2024
Liberia LBR
125
23.3%
2024
Guinea GIN
117
32.6%
2024
Zambia ZMB
115
37.5%
2024
Somalia, Fed. Rep. SOM
115
44.5%
2024
Malawi MWI
113
49.2%
2024
Tanzania TZA
113
37.2%
2024
Congo, Rep. COG
108
20.6%
2024, 2021
World Bank, World Development Indicators World Bank, World Development Indicators
People using at least basic sanitation services (% of population)
World Bank · CC BY 4.0 · updated quarterly
How this was computed
Data used: most recent value in 2010-2025; values come from 2015–2024. 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 Adolescent fertility and Basic sanitation
This page shows that two measures go together. It does not show that Adolescent fertility changes Basic sanitation, or the reverse. These figures also describe countries, not individual people. See the ecological fallacy.
More links with Adolescent fertility or Basic sanitation