Lesson 4 - Quantitative Analysis (Population Estimate) Flashcards
Linear Method
uses the rate of growth (or decline) in population over a period of time to estimate the current or future population. For example, if the population of Plannersville has grown an average of 1000 people per year over the last 20 years, this same rate of growth would be applied to the future.
Exponential and Modified Exponential Method
uses the rate of growth (or decline) in population over a period of time to estimate the current or future population. For example, growing 2% per year for 20 years. Two percent of 2,000 people is larger than 2% of 1,000 people. The result is a curved line. While a modified exponential projection assumes there is a cap to the change and that at some point the growth will slow or stop, resulting in a 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
uses available data to estimate the current population. For instance, the average household size is 2.5 according to the U.S. Census. If 100 new single-family building permits are issued this year, approximately 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
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.
This ratio is used to project the current or future population. For example, the 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.
The cohort survival method provides the most accurate population projection, but requires a large amount of data.
Cohort Survival Method
uses the current population plus natural increase and net migration to calculate a future population. The population is calculated for men and women in specific age groups.
Population Pyramid (Cohort Survival Method)
The results of this analysis can be presented in both numerical and graphic form. A graphic presentation with male cohorts on one side and female cohorts on the other will look like a pyramid with many people on the bottom (“birth cohort”). The number of people in each group declines with age.
Time Intervals (Cohort Survival Method)
Specific time intervals are used, such as five or ten years. The smallest time interval for which an estimate can be made is the length of time it takes for all members of an age cohort to age (e.g., age 10 - 14) to the next age grouping (e.g., age 15 - 19). All of the cohorts must have the same interval since each group must pass from one cohort to the next with nobody left behind over the course of the analysis.
Natural increase (Cohort Survival Method)
the difference between the number of children born and the number of people who die during one time interval. The analysis, however, is being done in terms of age-cohorts for each sex. Children can only be born into the first cohort, but people die in all of the cohorts, including the birth cohort. Children are born only to women of childbearing age, which means young girls and post-menopausal women have no direct effect on the number of children born.
Birth and Death Rates (Cohort Survival Method)
published by the state in the Vital Statistics of the United States through the U.S. National Center for Health Statistics. This information can be found at state offices as well, and is available by age cohort. The Death rate is the number of deaths per 1,000 people. The Crude Birth Rate is the total number of births per 1,000 people. The General Fertility Rate is the number of babies born per 1,000 females of childbearing age. The Age-Specific Fertility Rate is the number of babies born per 1,000 females in a given age group.
Net Migration (Cohort Survival Method)
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 pattern 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. Migration rates can be obtained from the state demographic office. In-Migration is the total number of people moving into a location. Out-Migration is the number of people leaving an area. The Migration Rate is simply out-migration minus in-migration.
