The regional growth forecast represents the most likely growth
scenario for the Southern California region in the future, taking
into account a combination of recent and past trends, reasonable
key technical assumptions, and regional growth policies. The
regional growth forecast is the basis for developing the Regional
Transportation Plan (RTP), Sustainable Communities Strategy
(SCS), Program Environmental Impact Report (PEIR), and the
Regional Housing Needs Assessment (RHNA). The regional growth
forecast is completed through the collaboration among the various
stakeholders.
SCAG projects three major growth indicators: population,
households, and employment, for the region. SCAG’s regional
forecast maintains the balance between employment, population,
and households due to their interrelationship, assuming that
employment growth is a driving force of regional population and
household growth. The employment-population-household (EPH)
forecast framework has been the basis for developing the regional
growth forecast for the SCAG region. The regional EPH framework
is implemented through three step process.
Step 1
The SCAG regional employment growth forecast is developed using a
top down procedure from the national population and employment
forecast. Regional employment is projected using the shift-share
model. The model computes regional employment at a future point
in time using a regional share of the nation’s employment.
Step 2
SCAG projects regional population using the cohort-component
model with an emphasis of an economic demographic modeling
context. The model computes population at a future point in time
by adding to the existing population the number of group quarters
population, births, and persons moving into the region during a
projection period, and by subtracting the number of deaths and
the number of persons moving out of the region. The patterns of
migration into and out of the region are adjusted to maintain the
reasonable difference between labor supply and labor demand.
Labor demand is estimated using the projected jobs for the
region.
Step 3
The SCAG region’s households are projected by using projected
headship rate. The projected households at a future point in time
are computed by multiplying the projected residential population
by projected headship rates. Headship rate is the proportion of a
population cohort that forms the household.
Age-gender-racial/ethnic specific household formation level is
applied to the projected population to estimate households.
The county growth forecast is also implemented in the EPH
forecast framework. The initial population and employment
forecasts are independently processed using their forecast
methods. The initial population and employment forecasts would be
further adjusted using the county level population-employment
ratio, with the consideration of labor supply and demand of each
county and inter-county commuting pattern.
