Population Estimate Flashcards
Linear Method
The linear method uses the change in population (increase or decline) over a period of time and extrapolates this change to the future, in a linear fashion.
For example, if the population of Plannersville has grown an average of 1000 people per year over the last 20 years, it would be assumed to grow by 1000 people annually in the future.
Exponential Method
The exponential method uses the rate of growth (or decline), i.e., the percentage change in population over a period of time to estimate the current or future population.
The population has been increasing by 2% per year for the last 20 years. This percentage change is extrapolated into the future. Two percent of 2,000 people is larger than 2% of 1,000 people. The result is a curved line.
Modified Exponential Method
Assumes there is a cap to the change and that at some point the growth will slow or stop, resulting in an S-shaped curved line.
The Gompertz Projection is a further modification of the modified exponential, where the growth is slowest at the beginning and speeds up over time.
Symptomatic Method
The symptomatic method uses any available data indirectly related to population size, such as housing starts, or new drivers licenses.
It then estimates the population using a ratio, such as the average household size (from the U.S. Census). Average HH = 2.5, data on 100 new single-family building permits that are issued this year, would yield an estimate of 250 new people will be added to the community.
Other sources of data for estimating population can include water taps, phone lines, voter registration, and utility connections.
Step-Down Ratio Method
The step-down ratio method is a relatively simple way to estimate or project population. This method uses the ratio of the population in a city and a county (or a larger geographical unit) at a known point in time, such as the decennial Census.
Population of Plannersville is 20% of the county population in 2000. If we know that the county population is 20,000 in 2005, we can then estimate the population of Plannersville as 4,000 (20%).
Distributed Housing Unit Method
This method uses the Census Bureau data for the number of housing units, which is then multiplied by the occupancy rate and persons per household.
This method is reliable for slow growth or stable communities but is less reliable in communities that are changing more quickly.
Cohort Survival Method
The cohort survival method uses the current population plus natural increase (more births, fewer deaths) and net migration (more in-migration, less out-migration) to calculate a future population.
The population is calculated for men and women in specific age groups
The cohort survival method provides the most accurate population projection but requires a large amount of data.
Natural increase
The difference between the number of children born and the number of people who die during the one-time interval. The analysis, however, is being done in terms of age-cohorts for each sex.
Net Migration
The difference between the number of people moving in and the number of people moving out. There are a variety of ways to calculate net migration.
It is possible to construct complex linear models to predict migration patterns for each cohort. However, it is also possible to use a simple migration rate that applies the migration rate from the previous period to the present projection.
