1. Summary and Closing Thoughts Greg Ball BSPS Council Member
Variant Projections
Summary and Closing Thoughts
Greg Ball
BSPS Council Member

2. Variants – what users do
“In the absence of any clear guidance ... users take one of two courses of action. Either they
reduce the uncertainty by ignoring all the scenario variations ... and simply take the central projection,
Or...
choose whichever end of the range justifies the taking of a particular policy position...”
Keith Woodhead 1985

3. Migration - a longstanding problem
“...imbalance between the relatively well-developed theory of demographic change and the relative paucity of explanation of migration...”
“...outstanding uncertainties ... as to how best to integrate and make consistent the estimation of population and migration change with the anticipated effects of policy.”

4. Approaches to internal migration
Demographic Multi-zonal (e.g. ONS)
Origin to Destination, based on recent patterns
Age the key determinant of flows
Changes in origin populations drive future migration flows
Consistent but inflexible
Local Demographic (e.g. POPGROUP)
Allows scenarios –e.g. Housing development rates
Effects on other areas??
Inconsistent across country
Integrated multi-zone models
E.g. East of England Forecasting Model

5. Local Housing Scenarios - Get in line!
Models assume an orderly queue.
Local household formation
International and cross-border migration
Internal migration between local authorities
To match housing scenario
Adjust internal flows (in and/or out)

6. Housing The True Story
There is no queue
Who pays wins

7. Issues for local scenarios
How can we better model relationships between policies for new housing development and migration?
What are the relationships, if any, between migration to and from an area and local household formation?
How do we model effects of local scenarios on other areas?