The Importance of Population Projections

1
Scenario Building

• The most critical part of the projection process
  is the delineation of a Projection Scenario.
• Projection Scenario The set of assumptions
  specified for the area being studied and for the
  projection method(s) utilized, across the
  projection interval.
• The projection scenario in many ways shapes the
  projections (and ultimately the forecast)
  generated. For all practical purposes The
  Scenario is the Forecast.
• There are many types of assumptions that must be
  laid out when undertaking population forecasting
• --Universal Assumptions (No wars, no
  catastrophic events) --Method-Based Assumptions
  (Future mortality rates) --Local Area-Based
  Assumptions (Future of fishing industry) --Region
  al-Based Assumptions (Floridas future growth)

2
Scenario Building Techniques

• They can be based on information gathered from
  monitoring, brainstorming, analogies, modeling or
  other activities. They should be developed
  rigorously and thoughtfully (Isserman)
• Typical aids utilized in developing useful
  scenarios
• 1) Historical Studies --Development of the
  area, Local history --Past rates of change in
  population, housing starts, births, etc. --Local
  planning initiatives, Policy environment
• 2) Consultation with Local Experts --Planners
  --Civic Leaders, both private and public
• 3) Choice of Control Units --Nearby
  counties --State
• Successfully developing a scenario is an
  inclusive process --Group inclusive
  --Community inclusive --Interest inclusive

3
Specifying Assumptions

• All projections are predicated on assumptions.
  These must be specified so that 1) producers of
  the projections can determine the internal and
  external consistency of their projections/forecas
  ts 2) consumers of the projections can
  understand the underlying logic/decisions
  behind these projections/forecasts
• Once the historical studies have been undertaken,
  interviews completed, and control units have been
  studied, it is time to provided a detailed
  specification of the assumptions.
• These should be as detailed as possible, laid out
  along the four assumption specification areas
  (Universal, Method-Based, Local Area-Based, and
  Region-Based assumptions).
• These can be included in a separate section of
  the projection document (relatively rare) or
  included throughout the document in appropriate
  sections (history in the history section,
  method-based in the methods section(s), and so
  on), which is more common.

4
A Forecast Scenario for Franklin County

• For URP5261 in 2003, the class contributed to the
  development of a population forecast for Franklin
  County (FC).
• FC is another Panhandle county soon to be
  transformed by St. Joe and this forecast was a
  primary input into the development of a
  Comprehensive Plan Update.
• As part of this project, a scenario was developed
  that identified 1) major factors contributing
  to population growth in FC in the period
  2000-2030 2) major factors likely to limit
  population growth in FC in the period
  2000-2030
• These factors were identified through a review of
  existing studies/documents, interviews with local
  experts, review of popular media (newspaper), and
  a review of other Panhandle county growth
  experiences in recent decades

5
FC Forecast Major Assumptions
1) No wars, sustained and long-term economic
recessions, or natural disasters will come to the
region and devastate the county. 2) SummerCamp
and other in-development projects will be built
out by 2010. 3) A state prison will be funded by
the state and be built by 2010 in the county.
This prison will bring 1,200 new residents to
the community in the form of prisoners. 4)
Additional large-scale residential projects will
be developed between 2010-2030. It was assumed
that an additional 1,750 new residential units in
master planned communities will be completed by
2020 followed by an additional 2,500 units
between 2020-2030.
6
Factors Promoting Growth in Franklin Co.

• Historic Population Growth in the County
• Continued Growth of the State and Region
• Emergence of Floridas Great Northwest as a
  Successful Brand for the Region
• Current Development Activity by St. Joe and Other
  Developers
• Future Development Activity by St. Joe and Other
  Developers
• Demographic Factors
• New State Prison in Franklin County

7
Factors Limiting Growth in Franklin Co.

• FCs Regional Location
• Infrastructure Issues
• Large Public Land Holdings
• St. Joe Land Holdings
• The States Role in Limiting Development in FC
• Anti-Development County Culture

8
Visualizing Franklin Countys Scenario
9
Franklin County Forecasts Using Different Methods
10
The Franklin County Forecast
11
Example Franklin Countys Combined Forecast
12
Evaluating Forecasts

• The three typical ways of evaluating a forecast
  are
• 1) Accuracy Correctness of the forecast
• 2) Validity Correctness of the model and
  causality
• 3) Constancy Validity over time and across
  situations
• But, forecasts are invariably incorrect, so maybe
  we should assess them on slightly different
  dimensions
• 1) Methodologically Sound
• --The forecast makes sense relative to the
  characteristics and assumptions of the
  methods
• 2) Internal Consistency
• --The forecast makes sense compared to
  historical demographic patterns
• --The forecast makes sense compared to local
  socioeconomic/ cultural characteristics
• 3) External Consistency --The forecast makes
  sense compared to contextual and/or
  comparison areas