Population Estimates Flashcards
Estimates
calculated for current population levels
Projections
calculated for future population levels
Migration
the movement of people into and out of a given study area.
Death Rate
the total number of deaths per 1000 people in the total population.
o In-Migration measures the total number of people coming in.
o Out-Migration measures the total number of people leaving.
o The Migration Rate is calculated by subtracting out-migration from in-migration. If the result is positive there is a net in-migration. If the result is negative, there is a net out- migration. The rate itself reflects total net migrants per 1000 people in population.
Historical Extrapolation
a basic method of projecting or estimating a population. This method assumes that past trends will continue into the future. As with any extrapolation, projecting too far into the future will result in erroneous conclusions.
Linear projections
assume that the population change will continue at the same numeric increase over the life of the projection. The formula for linear projections is y=a+bx. The result is a straight line on the graph.
Geometric projections
assume the rate of change remains constant., resulting in a curved line. The formula is y=abx
Exponential projections
assume that the population change will change exponentially over the life of the projection. The formula is y=aebx. The result is a curved line on the graph.
Modified Exponential projections
assume that the population change will change exponentially over the life of the projection, but the assumption is subject to an absolute cap on the change. The formula is y=c+abx. The result is again a curved line, but the upper or lower limit modifies the line into an azimuth.
Gombertz projections
modified exponential projections on steroids. It is used to project a change in direction over time. Formula: Yc = ca ^(bx)
Polynomial projections
calculated y=a+bx+cx2+dx3+ … xn
Ratio Method
compares the study area (i.e. a City) to a larger known entity (i.e. a State). The method is good for point in time comparisons as well as comparing relative changes over time.
Cohort Component (aka Cohort Survival)
population projections are commonly used to predict what the population will be for a given area in the future. The projection is based on past trends and data. They are heavily dependent on the birth rate, death rate, and migration rate (see terms above), and give an easily interpreted visual picture of the distribution of the population. On the following page are examples of “population pyramids.”
Distributed Housing Unit Method
based on housing data as follows: POPULATIONT = HOUSINGUNITST * OCCUPANCYRATE * PERSONSPERHOUSEHOLD
The Housing Unit Method
Housing data from the last Census is used as a base. This data is then adjusted using subsequently issued building, demolition, and conversion permits for housing.
