Guides
Short guides to reading population numbers correctly, each with figures from the UN data.
- Age percentile: what share of people are younger than youWhat an age percentile means, how it is calculated from population by single year of age, and why it changes with the year and the country.
- How to read a population pyramidWhat the bars, the two sides and the shape of a population pyramid show, with the pyramids of Niger, Japan and the world from UN data.
- Birth cohort or age group: two ways to group people by ageThe difference between a birth cohort (everyone born in the same year) and an age group (everyone of the same age on a date), and how to convert one into the other.
- Estimates and projections: what the population numbers for past and future years meanWhy population figures for the past are estimates, why figures for the future are projections, and how Anthrotempo labels each.
- Population reference dates: 1 January, 1 July and calendar yearsWhy population numbers refer to a date, why the UN gives both 1 January and 1 July figures, and how births and deaths are counted over a calendar year.
- Generation names and their birth yearsWhich birth years belong to Baby Boomers, Generation X, Millennials and Generation Z, where the boundaries come from, and why Anthrotempo uses them for years only.
- Percent and percentage points: two ways a share can changeWhy a share that goes from 10 % to 12 % has risen by 2 percentage points but by 20 percent, and how Anthrotempo reports changes in shares.
- How days alive are countedHow Anthrotempo counts the days and weeks you have lived, where the count starts, how leap years are handled, and what happens to a 29 February birthday.
- Reading development indicators: internet use, electricity, literacy and the HDIWhat the World Bank internet, electricity and literacy indicators and UNDP’s Human Development Index measure, who produces them, and how to read their years.
- Why missing data mattersWhy a missing value is not zero, how gaps in the data can mislead comparisons, and the rules Anthrotempo follows when a source has no value.
- Period and cohort life expectancy: what the number really measuresWhy life expectancy at birth describes the death rates of one year rather than how long anyone will live, and how it differs from the life expectancy of a birth cohort.
- Remaining life expectancy: why it is longer than you might thinkWhat remaining life expectancy at a given age means, why people who have reached an age can expect to live beyond the life expectancy at birth, and what the number does not say.
- Migrant stock and migration flow: two different numbersThe difference between the number of international migrants living in a country and the number of people moving in a year, how countries count migrants, and which measure Anthrotempo shows.
- Ageing and dependency ratios: how the numbers are calculatedWhat the old-age and child dependency ratios measure, how they are calculated from the population by age, and why they describe age structure rather than who works or who depends on whom.
- How cities are defined: one rule for every countryWhy national definitions of a city differ, how the UN degree of urbanisation draws cities, towns and rural areas on a population grid, and what that means for the numbers on Anthrotempo.
- Projection variants and uncertainty intervals: not the same thingThe difference between the UN’s projection variants, which change one assumption, and its prediction intervals, which say how uncertain the main projection is, with the numbers for 2100.