Glossary

Glossary

Life expectancy at birth (e0)

The average number of years a newborn would live if the age-specific death rates of one year applied throughout life. A period measure, not a prediction for a person.

Life table

A table of age-specific death rates for one population in one period, from which survival, life expectancy and the age distribution of deaths are computed.

qx

The probability that someone alive at exact age x dies before reaching x+1.

lx

The number of survivors at exact age x out of a notional birth cohort, usually 100,000.

Under-5 mortality (q5)

The probability that a child born in a given period dies before turning five, expressed per 1,000 live births.

Infant mortality

Deaths before the first birthday, per 1,000 live births.

Total fertility rate

The number of children a woman would have if she experienced the age-specific fertility rates of one year throughout her life. Replacement level is about 2.1.

Crude birth rate

Births in a year per 1,000 people alive. Affected by the age structure, so not a measure of family size.

Sex ratio at birth

Male births per 100 female births. The biological norm is about 105.

Income quintile

A fifth of a distribution. Quintile 1 is the poorest fifth of households, quintile 5 the richest.

Gini index

A measure of inequality from 0 (everyone the same) to 100 (one household has everything).

PPP international dollars

A currency unit adjusted so that one unit buys the same basket of goods in every country. Comparisons across countries use it; comparisons within a country do not.

Quantile

The point in a distribution below which a given fraction of observations fall. The 40th percentile is the 0.4 quantile.

δ (delta)

The cumulative survival-quantile shift produced by a life's choices, capped per country and sex so the effect cannot exceed the calibrated bound.

Tier A / B / C

Our label for how a value was obtained: observed (A), nearest observation within twelve years (B), regional median (C).

Median

The middle value: half the observations fall below it.

Cohort

A group that shares a defining event in the same period — here, everyone born in the same year.

Period vs cohort measure

A period measure describes one year's rates; a cohort measure follows one group through life. They differ whenever rates change over time.

Net migration

Immigrants minus emigrants in a period. Positive means more people arrived than left.

Urban share

The proportion of the population living in areas the country classifies as urban. National definitions differ.

Simulation

A rule-based model run forward. Here: a birth drawn from published distributions, then a life stepped year by year under published mortality.

Now live one

The odds on this page describe populations. The game draws one birth and plays that life forward, year by year, from the same tables.