GLA 2024-based trend population projections

Citation: © GLA 2024-based demographic projections

For questions about the projections or advice on their use, email the team at:  demography@london.gov.uk

Publisher information:
City Data Team
City Intelligence
Greater London Authority
City Hall, Kamal Chunchie Way, London, E16 1ZE
https://www.london.gov.uk/

# Notes:
1. All population estimates and projections relate to mid-year of the indicated year.
2. Births, deaths & migration figures relate to the twelve-month period ending at mid-year of the indicated year.
3. Ages in the components of change data refer to the age that an individual would have been at the end of the annual period, rather than at the time the event happened.
4. The label ‘90’ in the single year of age outputs refers to the age category ’90 years and over’
5. Data relate to local authority district boundaries as they existed in December 2023
6. Data are provided with limited rounding to facilitate their onward use. The apparent precision of data should not be mistaken as a declaration of accuracy.  All outputs should be considered as containing significant levels of uncertainty. Totals may not match due to rounding.
7. Population data are for the ‘usually resident population’ based on the United Nations definition and includes international arrivals expect to be present for at least a year. International migration data are based on the UN definition of long-term international migration. Internal migration includes both moves within 8. England and Wales and moves to and from Scotland and Northern Ireland
9. Birth, death, and internal migration estimates for past years are taken from published ONS estimates. Population and international migration are modelled estimates produced by the GLA. These modelled data reassign non-standard components of change from the official series (e.g. unattributable population change, and other adjustments) to international migration. Population and international migration estimates for children are further adjusted to better fit with observed changes in pupil and patient data.
10. Data up to mid-2024 are estimates and for subsequent years are projections.
11. The projections were produced after the publication of the ONS 2025 mid-year population estimates, but take no account of the results for 2025. However, they do include the revisions made to estimates for earlier years that were introduced as part of the publication.
12. Additional variants of these projections are available. We recommend that users do not rely on a single projection, but consider the results of multiple variants as well as alternative sources, such as the Subnational Population Projections published by the Office for National Statistics. 

# Variants

Projections are assigned codes that identify the fertility, mortality, and migration assumptions used, e.g.  “h25pt13”. A brief explanation of these codes is provided below. Additionally, the included file “config.txt” provides a summary of the internal model configuration file used to generate the projection.   

The core variants are also referred to as: “low”, “central”, and “high”. For the current round these labels are equivalent to:
- low = llt10
- central = ppt13
- high = hht15

## Fertility
The first part of the code identifies the fertility scenario. 
The letter “p” designates the use of the principal/central scenario. This is current based on the on the median outcome of a set of simulated forecasts. 
Low and high scenarios are designated by the letters “l” and “h”. If they are followed by a number, this designates how far from the median of the forecast distribution the scenario lies, e.g., the scenarios h25 and l25 cover 25 percent of the distribution, h75 and l75 cover 75 percent.
“l” and “h”, without following numbers are equivalent to “l50” and “h50” respectively.

## Mortality
The second part of the code identifies the mortality scenario:

“p” - principal/central
“l” - low life expectancy (i.e. high mortality)
“h” - high life expectancy (I.e. low mortality)
“n” - no improvement in life expectancy

These are based on the 2024-based NPP scenarios for England

## Migration
The third part of the code identifies the migration assumption. Typically the projections are based on an average of the last x years of international migration flows and internal migration rates.
When this is the case, the scenario is identified by the letter “t” followed by the length of the period, e.g.

t10 = average of last 10 years
t15 = average of last 15 years