| Technical
Notes: Population Projections
for Cities and Municipalities To project
population of cities and municipalities, the ratio method,
rather than the cohort component method, was utilized because
of the unavailability of data on fertility, mortality and
migration at the city/municipality level.
The ratio method of estimating the future
population of cities and municipalities makes use of the levels
and trends in the ratios of the population of cities and municipalities
to the population of their respective provinces observed in
previous censuses. These ratios are then projected on the
assumption that after some time stability will be attained.
In the present application, all cities and
municipalities comprising a province were classified according
to the trend of their ratios as observed in the 1970, 1980,
1990 and 1995 censuses. The four classifications are the following:
Type I - cities/municipalities that showed
unidirectional trend in their ratios (either increasing
or decreasing) throughout the observation period.
Type II - cities/municipalities that had
unidirectional trends only during the last two intercensal
periods.
Type III - cities/municipalities that
had unidirectional trends only during the first two intercensal
period.
Type IV - cities/municipalities with erratic
trends.
For each type of city/municipality, the
initial rates (r) at which the ratios will change were computed
as follows:
1. For a type I city/municipality, the initial
rate of change is equal to the geometric mean of the observed
annual rates of change of the ratios for the three intercensal
periods.
2. For a type II city/municipality, the initial
rate of change is equal to the geometric mean of the observed
annual rates of change of the ratios during the last two intercensal
periods.
where I (x)
= 1 if r80-90 > 0 and r90-95 > 0
= -1 otherwise
3. For a type III city/municipality, the
initial rate of change is equal to the geometric mean of the
observed annual rates of change of the ratios of the first
two intercensal periods.
where I (x)
= 1 if r70-80 > 0 and r80-90 > 0
= -1 otherwise
4. For a type IV city/municipality, the initial
rate of change is equal to one half the annual rate of change
in the ratios of the last intercensal period.
It was assumed that for all cities/municipalities,
r would gradually reduce so that they would all become zero
around 95 years from the base year, which is 1995. Based on
this assumption, a schedule of ratios was derived for each
projection year using the following formula:
where: = ratio
of the population of the city/municipality to that of the
province in 1995
= ratio of the population of the city/municipality to that
of the province for the kth year from 1995, and
= initial rate of change in the ratios.
Projected ratios are finally adjusted such
that the ratios of all cities/municipalities comprising a
province sum up to 1.0.
back to top
|
For your comments, suggestions and/or data request, you may contact:
