An overview of ONS's population statistics

Population statistics describe the demographic characteristics of the UK population.

These include statistics on the size, structure and geographic distribution of the population, on the factors driving population change (births, deaths and migration) and on topics such as families and older people.

This overview focuses on statistics published by the Office for National Statistics (ONS).

Where these statistics cover only part of the UK, similar statistics for other parts are often published by the relevant statistical agency - namely National Records of Scotland; the Welsh Government; and the Northern Ireland Statistics and Research Agency.

The population statistics published by ONS can be split into six groups:

The census

The census which has been conducted near the start of each decade since 1801, provides very detailed estimates of the 'usually resident' population as it was on Census Day.

These estimates can be selected by characteristics - for example, country of birth or marital status, and can be provided for small areas.

The census aims to collect information from every member of the population (in practice, adjustments are made to ensure that people who are not recorded on a census questionnaire are adequately reflected in the census results).

This means that the census has the advantage of providing sufficient numbers of smaller groups of the population - such as minority ethnic groups - for analysis.

Census estimates have the disadvantage of becoming outdated as the decade passes but can provide many statistics not available from other sources.

The first results from the 2011 Census were published in July 2012 and more information on the plans for further outputs is provided in the Census Output Prospectus.

ONS has established the Beyond 2011 programme to investigate and develop alternatives to the traditional census for 2021.

Population estimates

Population estimates relate to the number of people who were usually resident in an area at the mid-year point.

As well as the main national and local authority mid-year population estimates there are a range of other sets of estimates which provide information on population subgroups such as:

• the very elderly

• the population by marital status

• the population by ethnic group

Population estimates are also provided for other types of geographic area, including:

• national parks

• parliamentary constituencies

• wards

• primary care organisations

• Super Output Areas

Population projections

While population estimates provide a picture of the population as it was last year, population projections provide a picture of the population as it may develop in future years.

The three sets of population projections published by ONS are the national projections for the UK and its constituent countries, the subnational projections for local authorities and higher areas in England, and the marital status projections for England and Wales.

In addition to these, projections of the numbers of households in England are published by the Department for Communities and Local Government. 

Vital statistics

Vital statistics cover:

• births

• deaths

• marriages

• divorces

• civil partnerships and dissolutions

• conceptions

• adoptions

• cancer registrations

• baby names for England and Wales

Migration statistics

Migration statistics relate to the number of people who change their place of usual residence.

Different sets of estimates cover international migration and migration within the UK.

The Long-Term International Migration (554.5 Kb Excel sheet) statistics provide estimates of the number of people moving into, and out of, the UK to live.

Additional tables provide information on which country migrants come from, or go to, the reason for migrating, citizenship and the expected length of stay.

This set of statistics is probably the one most quoted when discussing international migration.

Whilst these statistics relate to flows of people, estimates of the total numbers of people of different countries of birth or nationality living in the UK (252 Kb Excel sheet) are also published.

Short-Term Migration statistics provide estimates of the number of people who enter or leave the country for less than a year and who would not generally be counted as a migrant.

Estimates of internal migration (that is, migration between areas in the UK) are published annually. 

Two other releases bring together a variety of statistics from across government to help build up a picture of migration.

These are the Migration Statistics Quarterly Report, which provides a straightforward presentation of the main migration statistics at the national level, and the Migration Indicators Suite (6.6 Mb Excel sheet) , which contains broadly similar information but in a form suitable for analysis for local authorities.

Demographic analysis

Demographic analysis brings together a range of statistics to provide a better understanding of the country's population.

• Life expectancy statistics - Life expectancy statistics combine population estimates and statistics on the number of deaths to derive an estimate of how long, on average, people of various ages are likely to live. These statistics include the decennial life tables, which are very detailed and centred on a census year; the interim life tables, which are published every year; period and cohort life expectancy tables, which use mortality rates from the national population projections to estimate how life expectancies may change in the future; and the life expectancy by local areas tables, which provide further detail for local authorities and, as experimental statistics, for wards

• Ageing - Analysis of ageing-related official statistics (including life expectancy figures, mid year population estimates, estimates of the very elderly and population projections) is undertaken to produce a number of outputs. These include the Focus on Older People release (published to coincide with UK Older People’s Day) summarising the latest analysis of official statistics on population ageing and the lives of older people; and Ageing in the UK - an interactive mapping tool which allows users to analyse the age structure of the population by providing ageing indicators such as median age, and sex ratios at older ages, at the national and local level

• Families statistics - Families analysis adds value to the information published on marriages, divorces and civil partnerships. More detailed analysis on these topics includes the proportion of marriages ending in divorce. An annual release is published on households and families in the UK, including statistics such as percentage of children living in lone parent families and the number of married versus cohabiting couples. Estimates of the cohabiting population are also produced every few years. Reports are published on topics of current interest such as civil partnerships (190.1 Kb Pdf) and partnership stability (255.1 Kb Pdf)

• Fertility statistics - The key role of the fertility team is to produce fertility assumptions for the national population projections, based on evidence from research. Fertility analysis also adds value to information published on births. The team publishes annual tables and reporting on cohort fertility (including childlessness), birth order, fertility among women born inside and outside the UK and male fertility, as well as frequently asked questions (232.1 Kb Pdf) . Reports are published on topics of current interest such as fertility and migration or fertility and partnership status