what is used to find specific populations within a database

Introduction

Course Objective

Develop skills to estimate the population size of a given locale

Expected Effect

Skills to estimate population size for two periods in fourth dimension, the current year and a year between census periods.

This lesson focuses on ways to estimate and project the population size of a locale. It discusses the departure betwixt estimating, projecting, and forecasting the population and provides guidelines for performing accurate estimations and projections. It demonstrates how to calculate both the current population size of a locale and the midyear population size between demography periods. The latter is necessary to summate vital rates such every bit the general fertility charge per unit and age-specific fertility rates for dissimilar time periods. The lesson concludes with the awarding of two estimation tools: an inter-demography technique for estimating the midyear population and a post-census estimation using the housing unit method.

five.1 Estimates, Projections, and Forecasts

What Is the Departure between an Estimate, a Project, and a Forecast?

A population estimate is a calculation of the size of a population for a year between census periods or for the current year. At that place are 2 types of estimation techniques: inter-demography and post-census.

1. Aninter-census interpretation is for a date between two census takings and unremarkably takes the results of the two censuses into account.
2. Apost-census estimate is typically conducted for the electric current year.

Estimates involve the use of data that are based on the following information:

• Components of population change, including migration, fertility, and mortality
• Census results
• Information that reflects modify in population size such as the number of housing units, postal or mailing addresses, registered voters, school enrollment, and users of metered water and other utilities.

A projection is a calculation of the size of the population for a future date in time. Population information for by, nowadays, and future conditions can exist used to make a projection nearly the population. While estimations tend to calculate the full population size of a locale, projections calculate the full population size as well as the size of various segments of the population. For example, the population accomplice projection method can be used to calculate the population size of males and females by 5-year historic period groups. The accuracy of estimation and project tools is based on the rules and assumptions that are embodied in the method used.

A forecast is a projection that includes judgment statements concerning the hereafter. Forecasting requires knowledge virtually past and present social, economic, and demographic trends. Planners who choose to forecast may modify the data employed in a projection to reflect their judgment of time to come trends. For example, if planners expect births to pass up in the hereafter, they can alter the age-specific fertility rates when projecting population by age and sex. The tools covered in Lessons v-8 do not include population forecasting. Population estimations and projections are based on the assumptions of the tools rather than judgments of future trends. In this case, information technology is much easier to explain the assumptions than it is to justify personal judgments well-nigh future conditions.

Estimates and projections can be forde jure (usual resident) orde facto (physically present) populations. In most cases, they are based on de facto populations. This data tin can exist divided into two categories:

Direct

data comes from census data and information on births, deaths, and migration.

5.two Interpretation and Projection Guidelines

Interpretation and Projection Guidelines

The quality of information and data for a given locale, as well as the ability of the data to run across the bones assumptions of the analytic method are key to performing accurate estimates or projections. Shryock and Siegel (1973) and Morrison (1971) adult the following guidelines for performing population estimations and projections:

1. More accurate estimates can generally be made for an entire land than for geographic sub-divisions of a country. It is easier to obtain migration information at the national level since international migration is usually recorded when individuals and families enter a country. This is not the case, however, for cities, towns, and districts, where migration information is collected as role of a census every x years.
2. More authentic estimates and projections tin can generally be made for the total population of an area than for the demographic characteristics of the population. The census is the only data source bachelor to project population past select attributes such equally age, sex, and occupation. More information sources are available to estimate or projection the size of the total population. When projecting or estimating total population size, it is possible to use several tools that are based on different information sources and compare the results.
3. Straight data are preferred to indirect data. Population information that is based on the components of population alter such as births, deaths, and migration, and methods that parallel demographic processes, may produce more accurate estimations and projections.
4. An estimate or projection should e'er exist checked by comparing it with another gauge or projection that employs an equally accurate or more authentic method.
5. The poorer the information quality and the longer the projection period, the less reliable are the results. 20-twelvemonth projections are non equally reliable as those of 5–ten years. In add-on, economical activities can influence in- or out-migration and lead to the rapid growth or decline of a locale. The surroundings also influences population change. For example, droughts and floods tin lead to major reductions in population size.
6. The most accurate projection is commonly based on a combination of methods. For example, apply two methods whose assumptions back up available information sources, and have an boilerplate of the two.
7. Never take for granted that a information series is correct, regardless of the agency providing it. Equally discussed in Lesson 4, always review a series of data and data over time to exist sure that it is consistent.
8. If a series of census information changes drastically over time, determine the cause. In some cases, census boundaries or data drove methods may have changed, rather than the bodily size of the population.

five.3 Estimation Tools

Estimation Tools

This section demonstrates how to calculate ii types of population estimations: the population size of a locale between demography periods and the current population of a locale. You may use Equation v-one to approximate the midyear population betwixt census periods, as well every bit the current population, provided that reliable information is available on the number of births, deaths, in-migrants, and out-migrants.

Equation v-1
Components of Demographic Modify

This equation will provide the most accurate population estimate. Notwithstanding, data on all three components of demographic alter are rarely available. Therefore, information technology is necessary to utilise other estimation methods. The methods presented in this lesson assume that reliable information is not bachelor on the components of demographic change, but that planners will have access to demography information and indirect information that reflects population change. Suggestions for other interpretation methods are included at the finish of the lesson.

Inter-Census Estimation: Midyear Population

The following estimation method is used primarily to estimate the midyear total population, or a subset of the population of a given locale.

Indirect

data include data thatreverberate changes in population size, such as school enrollment, housing units, gas and electric meters, employment statistics, tax information, voter registration, and postal addresses.

Assumptions

This method assumes that yearly changes in the population size are equal. It also assumes that population change betwixt the two census periods is linear. Plotting several census periods with fourth dimension on the horizontal line (Ten-axis) and population size on the vertical line (Y-axis) results in a straight line between the points.

When to Use this Tool?

This estimation tool is primarily used to calculate the midyear population for vital rates such as the crude nascency or death charge per unit, age-specific fertility or death rates, and the general fertility rate.

Equation five-2 can be used to estimate the population size of a subset of the population, or the total size of a population between census periods.

Equation 5-2
Estimating the population size betwixt two census periods

Equation v-3
Crude Birth Rate

For case, in order to calculate the rough nascency rate for Durham County, Northward Carolina for the twelvemonth 1999, it is necessary to estimate the midyear population for 1999. Equation five-3 provides the calculation for the crude birth rate.

The date of the census taking for both periods is April 1. The engagement of the midyear population is July ane. Note that the midyear month is unlike from the census calendar month. These differences are taken into account when calculatingn. The following example demonstrates Equation v-2 in estimating the midyear population and the adding of the rough birth rate.

Example of Equation v-three

Practise 5-1

Calculate the crude birth charge per unit for Durham County in 1998, where the number of births is 3,288. Hash out the limitations of this estimation tool.

Post-Demography Interpretation: Housing Unit Method

The housing unit of measurement method uses information on housing to estimate the total population size for a locale.

Assumptions

The housing unit method assumes that a alter in the number of occupied housing units reflects a change in the population size.

When to Use this Tool?

Use this tool to perform an estimate for an surface area with little or express demographic data. This method tin be used for districts or counties, cities, and towns. Information technology tin besides be used for rural areas provided that the necessary data on housing units and average household size tin exist nerveless for the locale. In add-on, it can be used to estimate the current population size also equally population size between census periods, provided that information can be obtained for the interpretation yr.

Data Needs

A census of population and housing is required. Census information is needed for the total number of residential housing units, number of vacant residential units, number living in group housing, and average household size. This information can besides exist obtained from surveys. In addition, data are needed on new building permits, demolitions activity, certificates of occupancy, and building conversions. Obtain this data from those agencies that are responsible for building inspections and housing.

The side by side section presents the summary equation for theHousing Unit Method tool, as shown in Equation 5-4. In addition, an explanation and calculation of the various components in Equation 5-iv are provided.

Equation 5-4
Housing Unit of measurement Method Summary Equation

Stages in the Housing Unit Method

i. Population living in group housing

Residents of grouping housing include individuals residing in institutional housing such as dormitories, military machine barracks, prisons, and patients living in long-term care facilities such as mental hospitals and nursing homes. Information technology also includes individuals and families living in non-institutional facilities such as boarding houses. In some countries, this data is collected equally part of the census. The accuracy of this estimate can exist improved by contacting institutions and boarding homes to collect information on the number of residents living in group housing. Ensure that the institutions contacted are within the geographic boundaries of the estimation surface area.

2. Occupied Housing Units

The calculation for occupied housing units is shown in Equation v-five.

Equation 5-v
Occupied Housing Units

A demography of population and housing, nonetheless, volition include data on the number of housing units. It is also possible to obtain this data from housing surveys. Note that a housing unit is not the same as a building. A housing unit is the place of residence for an private, family, or a group of unrelated adults and children. For small locales, such as a boondocks or village, information technology may be possible to actually count the number of housing units.

If census information is available, update the information on the number of occupied housing units. This is a ii-stride process. Available housing is constantly changing as new units are built and old ones are destroyed or converted to other uses. The start step is to tape changes in the number of housing units from the time of the census taking to the estimation twelvemonth equally shown in Equation 5-half dozen.

Equation 5-6
Changes in the Number of Housing Units Between 2 Census Periods

Net conversions are included because a edifice'southward use tin change several times during its existence. Households may decide to turn a abode into a concern and find a new place to alive. Conversely, buildings that were created for commercial or industrial use tin exist converted into apartment units.

The 2nd step, once data is obtained on the number of housing units, is to determine the number of housing units occupied by people, every bit shown in Equation 5-vii. For this adding, multiply the number of housing units by the occupancy rate. To practise this calculation, information technology is necessary to determine the occupancy rate.

Finding the occupancy rate:

Equation 5-7
Occupancy Charge per unit

In some countries, the vacancy charge per unit tin be obtained from census reports, every bit shown in Equation 5-viii.

Equation five-8
Vacancy Charge per unit Using Census Data

These are alternative ways to obtain vacancy rates. In cities, towns, and rural areas where a loftier percentage of the population legally apply utilities such as electricity and water, information should be available from a utility company or authorities office to determine active and inactive use of a given utility. Make certain this information matches the geographic locale for the estimation surface area.

Equation 5-9
Calculating a Vacancy Rate from Utility Accounts

iii. Average Household Size

The number of occupied houses is multiplied by the boilerplate household size. The results provide an estimated population size of those living in residential units. The average household size tin can be obtained from demography information or household surveys.

Problems with the Housing Unit Method:

First, information technology is difficult to obtain reliable information because some countries do not crave building permits. Second, non all residential edifice permits are for housing units. In some countries, residential permits are required to add a garage, a storage shed, or another room to existing housing. Also, the fact that a permit is issued in a particular twelvemonth does not mean that a unit will be built in that year. To increment the accuracy of data based on edifice permits, use certificates of occupancy every bit an added cheque; many countries require these before a tenant moves into a residential unit.

Problems in collecting demolition data:

Inspectors may non signal the number of units within a construction that is existence torn down. The identity of the person/grouping who demolished the structure must be adamant in order to calculate how many units were used for residential housing. Issues may also be with conversion data. Not all households report conversions or changes in how a domicile is being used. In some locales, families can discover other places to live and apply an unabridged house for a pocket-size business.

The bottom line for all interpretation and projection tools:

Make up one's mind if it is possible to collect the required information and the feasibility of working within with the basic assumptions of the method.

5.4 Summary Equations

The following steps demonstrate how to use the housing unit of measurement interpretation tool. This example uses data from Table v-1 to estimate the population size of an urban district for yr 2000.

Table 5-ane: Sources of Information for Using the Housing Method to Gauge the Population Size of an Urban District for the Year 2000
Source of Information	Data
Demography Information Occupied housing units, 1990 Vacant housing units, 1990 Average household size, 1990 Population in grouping housing, 1990	58,360 2,237 2.42 seven,825
Building Inspector'southward Office Building Permits, 1990–2000	18, 247
Demolitions Private sabotage companies, 1990–2000	315
Building Conversions From industrial to apartment units, 1990–2000 From housing to commercial apply, 1990–2000	20 10

Step ane:

Use the actual census count for 1990 on grouping housing and theHousing Unit of measurement Method Summary Equation as presented in Equation five-four to judge the population size. The population living in group housing = vii,825. When possible, place the types of institutions used past the census, contact each institution to determine if it still exists, and obtain the number of residents for each type of facility for the estimation year.

Step 2:

Use Equation v-ten to summate the number of housing units. Data for this instance tin be found in Table v-1.

Equation five-10
Housing Units

Stride 3:

Next, obtain an occupancy rate as presented in Equations five-7 and 5-8 to make up one's mind how many of the housing units are occupied. Demography data from Tabular array 5-one is used to calculate the vacancy rate that is presented in Equation 5-11.

Using Equations 5-7, v-8, and 5-10

Pace 4:

Obtain the boilerplate household size using 1990 census data every bit indicated in Table v-1.

Putting it all together. The results are shown in summary equation 5-13.

Instance of the Housing Unit Method Summary Equation (Equation 5-4)

Annotation that the actual population of the urban district in 2000 was 181,854.

Exercise five-2
What can be done to improve this estimation and bring it closer to the census population?

• Review the process of calculating this estimation technique. Call back nearly the data sources employed.
• Describe how to improve the estimate for the urban district.
• What type of information tin be used?
• Where could the information be obtained?

5.5 Discussion

This lesson demonstrated the use of two estimation tools that require express data. Information technology provided guidelines for selecting and conducting population estimations and projections. These are not the only estimation tools that are bachelor; additional project tools will be provided in Lesson 6. An excellent spider web site demonstrating the use of a range of estimation techniques may exist establish at the United States Agency of the Demography. This site is particularly useful in explaining the housing unit estimation tool.

Exercise Answers

Answer — Practise 1

Population Judge for 1998 = 152,785 + 99 / 120 (181,835 - 152,785)

Population Estimate for 1998 = 152,785 + (.825)(29,050)

Population Estimate for 1998 = 176,751

Crude Nascency Rate for 1998 = (iii,288 / 176,751) x 1,000 = 18.six

The tool assumes that the aforementioned number of people is added to the population each year and that growth is linear. In virtually cases, locales practise non increase by the same number of residents each yr.

Respond — Exercise ii

Considering the estimation for the urban district relied heavily on 9-year-old census data, information technology was necessary to place other sources of information. For example, effort toamend the information for group homes. This can be done past identifying institutions, boarding homes, and long-term hotels that provide housing for individuals and households and collecting information on the total number of residents in each blazon of group housing.

Census data was used to summate the vacancy rate, but housing surveys could also provide information. Check with the housing division in the district planning office or with nearby university faculty in sociology, geographic, and planning departments to meet whether studies are available. If a high percentage of the population uses electricity legally, utility information can be used to judge the vacancy rate. If multiple information sources are available, utilise an average of the 2 best vacancy rates.

At that place are several ways to ameliorate the data on building permits as well. Verify whether the permits issued during the estimation period were actually used, and make sure they were used for housing units versus other types of structure, such as adding a room or garage to an existing firm. Substitute certificates of occupancy for building permits if bachelor. These certificates are needed in order for new residents to movement into a housing unit.

Information ondemolished buildings is oft bachelor from private companies that demolish buildings. In the example, information was not available on the number of housing units destroyed for each structure. In this case, it is possible to better the interpretation, by identifying where buildings were destroyed and asking neighbors nearly the number of housing units that were in the buildings.

Information onaverage household size was taken from the census. Household survey data could have been obtained from different studies to find changes in household size and and so averaged.

It is too possible to appraise the quality of available census data. How did the demography count the homeless? Did it collect information on those living in slum and squatter settlements? Try to make up one's mind how many people live in makeshift or temporary housing in squatter settlements. In most cases, makeshift housing appears overnight. If these types of housing units are non destroyed by government on a regular basis, include them in the count. Also, check with institutions that provide services to the homeless to get an thought of how many to add to the estimation.

These results can be compared with other estimates to encounter if they are also low or high (see Lesson 6 for other tools that tin exist used to gauge the current population).

These are merely a few examples of estimating. Experiment with different ideas to improve the accuracy of this tool in your locale.

References

George W. Barclay, "Rates and Ratios,"Techniques of Population Analysis (New York: John Wiley & Sons, 1958) 16–55.

Peter A. Morrison,Demographic Data for Cities: A Transmission for Estimating and Projecting Local Population Characteristics (Santa Monica, CA: Rand, 1971).

Norfleet West. Rives and William J. Serow, Quantitative applications in the social sciences: Paper 39,Introduction to Applied Census: Data Sources and Estimation Techniques, (Newbury Park: Sage Publications, 1984).

Henry Southward. Shryock and Jacob Due south. Siegel, "Population Estimates,"The Methods and Materials of Census, (Washington, D.C.: Agency of the Census, 1973) 725–770.

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