poulation forecasting
TRANSCRIPT
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POPULATION FORECASTING
METHODS
Dr. Pallavi Badry
Associate Professor
V.J.I.T Hyderabad
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POPULATION FORECASTING :-
Calculation or prediction of some future
events as a result of study and analysis of
available records or data is the
population forecasting
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Factors affecting population
growth
Design of water supply and sanitation scheme is
based on the projected population of a
particular city,
Factors affecting changes in population are:
increase due to births
decrease due to deaths
increase/ decrease due to migration
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METHODS :-
1. Arithmetical Increase Method
2. Geometrical Increase Method
3. Incremental Increase Method
4. Decrease Rate Of Growth Method
5. Simple Graphical Method
6. Graphical Comparison Method
7. Master plan method
8. Apportionment/zoning Method
9. Logistic curve Method
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ARITHMETICAL INCREASE METHOD :-
This method is based on the assumption that the rate of change of population with time is constant.
This method is suitable for large and old city with considerable development. If it is used for small, average or comparatively new cities, it will give lower population estimate than actual value.
In this method the average increase in population per decade is calculated from the past census reports. This increase is added to the present population to find out the population of the next decade.
Thus, it is assumed that the population is increasing at constant rate.
Mathematically,
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Geometrical Increase Method (GEOMETRICAL PROGRESSION METHOD)
In this method the percentage increase in population from decade to
decade is assumed to remain constant.
Geometric mean increase is used to find out the future increment in
population.
Since this method gives higher values and hence should be applied
for a new industrial town at the beginning of development for only
few decades.
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INCREMENTAL INCREASE METHOD
suitable for an average size town under normal condition where the growth
rate is found to be in increasing order.
Increase in increment is considered for calculating future population.
The incremental increase is determined for each decade from the past
population and the average value is added to the present population along with
the average rate of increase.
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GRAPHICAL METHOD
Populations of last few decades are correctly
plotted to a suitable scale on graph.
The population curve is smoothly extended
for getting future population.
This extension should be done carefully and it
requires proper experience and judgment.
The best way of applying this method is to
extend the curve by comparing with
population curve of some other similar cities
having the similar growth condition.
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COMPARATIVE GRAPHICAL METHOD
In this method the census populations of cities already developed under similar conditions are plotted.
The curve of past population of the city under consideration is plotted on the same graph.
The curve is extended carefully by comparing with the population curve of some similar cities having the similar condition of growth.
The advantage of this method is that the future population can be predicted from the present population even in the absence of some of the past census report.
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MASTER PLAN METHOD
The big and metropolitan cities are generally not developed in haphazard
manner, but are planned and regulated by local bodies according to master
plan.
The master plan is prepared for next 25 to 30 years for the city.
According to the master plan the city is divided into various zones such as
residence, commerce and industry.
The population densities are fixed for various zones in the master plan.
From this population density total water demand and wastewater generation
for that zone can be worked out.
By this method it is very easy to access precisely the design population.
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LOGISTIC CURVE METHOD
This method is used when the growth rate of population due to
births, deaths and migrations takes place under normal situation
and it is not subjected to any extraordinary changes like
epidemic, war, earth quake or any natural disaster, etc., and the
population follows the growth curve characteristics of living
things within limited space and economic opportunity.
If the population of a city is plotted with respect to time, the
curve so obtained under normal condition looks like S-shaped
curve and is known as logistic curve
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LOGISTIC CURVE METHOD
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Tutorial
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Solution
Step:1 To find out the increment from the population data
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Population curve from the data given
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Step2 : To find the average increment/rate of change of population wrt
time from the population increment
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Step3 : to estimate the population at the respective year from the
formula of arithmetic increase method
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Forecast the population for the year 2021, 2031 and 2041
using Geometrical progression method
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Step 2 : to estimate the Geometrical increase rate of
growth
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Step 3: To find out geometric mean (IG or r)
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Step 4: Population forecasting
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INCREMENTAL INCREASE METHOD
Step 1: Extract the population data
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Step: 2 Find the increment in population (X)
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Step: 3 Find the incremental increase (Y)
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Step: 4 Find total and average of increase and
incremental increase
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Step: 5 Population forecasting
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Comparative graphical method
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Given data
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Graphical representation of population
for different cities
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Average mean of all
population
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Extend the population curve
2010 79400
2020 85400
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Problem 5
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Important Formulae used in method
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Population at saturation Ps
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Problem 6