Composition Population Forecasting Models, Migration Models

8/3/2019 Composition Population Forecasting Models, Migration Models

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Forecast:A statement of the most likely futureEvaluation of various possible assumptions

and determination of most probableForecasting is the art of predicting thefuture.

Population forecast: predicting the changes inthe population


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There is a need for the County to accurately forecastpopulation over time for the short and long-term planninghorizon.Current methods may underestimate population growth forboth short and long term planning and has the potential forinfrastructure to fall behind the demands of population. Thisinfrastructure can be road network, utilities, schools,recreational facilities and public services.over-estimating population could result in large-scale capitalinvestments that are under utilized with little returns.There are more accurate applications to forecast growth than thetypical linear extrapolation, like the growth model to forecastthe need and location for current and future improvements.


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Cohort Component Model Simple Curve fitting or Extrapolation Model Exponential Model

Gompertz (Sigmoid or Logistic) Model.ExtrapolationEconomic-demographic modeling


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Cohort Component Model:1. This method ages the various age groups or

cohorts in the population into the future andapplies the appropriate birth and death rates.

2. It also requires an estimate of the level of in-and-out migration.

This method can be quite accurate whenforecasting population up to ten or twenty yearsinto the future.Future population =Present population + Births

Deaths + In-migration - Out-migration + Net foreignimmigration


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COHORTS are populationgroups

Defined by age, gender,and often race orethnicity

Typically five-year agegroups 0-4, 5-9, . . . ,through 85+For example, women

aged 20-24

COMPONENTS refer topopulation changeNatural increase is births

Minus deathsGross migration refers to

In-migration and outmigrationNet migration is

inmigration minusoutmigrationU.S. Statistics distinguish

Domestic migration andinternational immigration


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In the cohort component population projections:births, deaths and migration are projected

separately by applying cohort specific rates of population divided into age and sex cohortsHowever, when high levels of in-migration areexpected over long periods of time, this model

becomes less relevant because it focuses on theaging of the current population, while providinglittle assistance in forecasting the critical rate of in-migration.


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This method plots past population levels overtime in a time series and then extends theline or curve by regression analysis into the

future to forecast future population levelsAnother shortcoming of this method is thatlong-term limits to growth (build out) are notfactored in.


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An exponential trend is one where the trendis increasing at a constant rate of changeeach year.

This compounding effect of a constant rateof growth can result in astronomicalincreases in forecasted population in the longterm.

While this type of trend in growth may existfor a period of ten years or even twentyyears, it cannot sustain itself for longerterms


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Many biological populations (including cities)tend to grow at a rate over time thatsimulates a logistic or Sigmoid Curve.

Population growth increases at an increasingrate over time until it reaches an inflectionpoint, then the increase in population growthis at a decreasing rate until it reaches uppergrowth limit


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The Sigmoid Model as illustrated in Figure 2-1, shows the upper limit, inflection point andthe rate of growth.

For example, the population increases at anincreasing rate up to the inflection point,then the population increases at a decreasingrate to build-out.

It should also be noticed that the greatestincrease in population takes place prior toand after the inflection point.


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Develop an equation that fits the trend in agiven variable population best, using datafor a particular period in the past, and use to

predict future trend in the variable


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There have been several models of proposed by various academiccommunities

They are like: simple migration model

Lees general model Gravity model Todero model Raven steins law Stepwise migration model Circular migration

Few models are discussed In this presentation ,they are as follows:

MIGRATION MODELS


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Decisions about migration are shaped by economic, social, and cultural

factors. Migration models formalize these determinants. They also

may describe the effects of migration at its origin and destination and the interactions between those effects.

Most formal migration models focus on economic

determinants: opportunities and constraints on income at migrant

origins (limited capital and technology, scarcity of employment, imperfect market environments), income opportunities at migrant destinations (demand

for migrant labor in urban centers), and migration costs (travel costs, networks of contacts

at prospective migrant destinations, border policies).


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Composition Population Forecasting Models, Migration Models