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Westminster Child Population Projections 2025

Interactive visualisation comparing Mid-Year Estimates with GLA 2024-based population projections for Children's Services.

About This Project

This Streamlit app was created to resolve confusion among Westminster Children's Services teams about 2025 child population estimates. Different teams were citing conflicting figures, which arose from referencing different age bands (0-15 vs 0-19), different projection variants, and potentially outdated documents.

What This Tool Shows

  • Interactive charts comparing actual Mid-Year Estimates (2023-2024) with GLA 2024-based projections (2025)
  • Three migration variants showing range of plausible outcomes:
    • 5-year migration trend (2019-2024 average)
    • 10-year migration trend (2014-2024 average) ⭐ RECOMMENDED
    • 15-year migration trend (2009-2024 average)
  • Gender breakdowns (optional toggle)
  • Full methodology with strengths and limitations

Key Findings

Recommended Figures for 2025 (10-year migration variant):

  • Ages 0-19: 34,705 persons
  • Ages 0-15: 25,516 persons

Range Across All Variants:

  • Ages 0-19: 34,705 to 34,897 (192 persons range)
  • Ages 0-15: 25,516 to 25,668 (152 persons range)

Projected Changes from 2024:

  • Ages 0-19: Decrease of 720 to 912 persons (depending on variant)
  • Ages 0-15: Decrease of 552 to 704 persons (depending on variant)

Methodology

Data Source: GLA 2024-based trend-based population projections (research outputs)

Base Year: 2024 Mid-Year Estimates (ONS, published July 2024)

Assumptions:

  • Fertility: Principal (central) assumption - held constant
  • Life expectancy: Principal (central) assumption - held constant
  • Migration: VARIED across three scenarios (5yr, 10yr, 15yr historical averages)

Why only migration variants?
This analysis focuses exclusively on migration variants because Westminster is a highly mobile borough where migration is the most volatile demographic component and the primary driver of uncertainty in child population projections.

Other GLA variants not examined:
The GLA produces seven projection variants in total, combining different fertility, life expectancy, and migration assumptions. This analysis examines only the three variants that hold fertility and life expectancy constant whilst varying migration assumptions.

Why GLA Projections?

Strengths:

  • ✅ Most recent data available (based on 2024 MYEs)
  • ✅ Incorporates latest migration trends
  • ✅ Transparent methodology
  • ✅ Widely used for planning across London boroughs

Limitations:

  • ⚠️ Labelled as "research outputs" - not yet quality assured
  • ⚠️ Projections are inherently uncertain - actual 2025 MYE may differ
  • ⚠️ The 2025 MYE won't be published until mid-2026
  • ⚠️ This analysis only examines migration variants

Files in This Repository

  • app.py - Main Streamlit application
  • requirements.txt - Python dependencies
  • README.md - This file

Updating the Data

When new data becomes available (e.g., 2025 MYEs in mid-2026):

  1. Edit app.py on GitHub
  2. Update the default_data dictionary (around line 155)
  3. Commit changes
  4. Streamlit will automatically redeploy within ~1 minute

Technical Details

Built with:

  • Python 3.9+
  • Streamlit 1.29.0
  • Pandas 2.1.3
  • Plotly 5.18.0

Data embedded in code - no external files or databases required.

Contact & Support

This tool was created for Westminster City Council Children's Services.

For technical issues with the Streamlit app, check the Streamlit documentation.

Last updated: December 2024
Data source: GLA 2024-based Population Projections (Research Outputs) | ONS Mid-Year Estimates
GLA Documentation: https://data.london.gov.uk/blog/gla-2024-based-population-projections-research-outputs/