Population Projection

Population projections are calculations which show the future course of  fertility, mortality and migration. They are in general purely formal calculations developing the implications of the assumptions that are made. Population Projection are logical and mathematical derivatives of the set of assumptions of fertility,mortality and migration behaviour.  Population projection, in the field of demography, is an estimate of a future population. In contrast with intercensal estimates and censuses, which usually involve some sort of field data gathering, projections usually involve mathematical models based only on pre-existing data may be made by a governmental organization, or by those unaffiliated with a government.

Importance of Population Projection:

1. future planning of social, economic and political aspects of the country
2. helps in long term planning and makes it successful
3. helps the need of new facilities in future and makes necessary arrangements
4. to formulate rules and laws on population
5. to find out the need of goods in the market and hence to make necessary arrangements for that
6. alternative for any types of statistics

Method of Population projection:

1. Linear growth function
2. Geometric growth function
3. Exponential growth function
4. Modified Exponential function
5. Logistic Curve function
6. Gompertz curve function

Migration

Migration is a geographical movement of people from one area to another during an interval and involving a change of residence.

Types of Internal Migration:
On the basis of time:
1.Permanent Migration (stayed more than 5  years during census)
2.Semi- Permanent Migration (1-5 years during the time of census)
3. Temporary Migration (6months to 1 year during census)
4. Seasonal Migration (less tan 6 months or seasonal)
 On the Basis of flow:
1. Rural To Urban Migration
2.Rural to rural migration
3. Urban to rural migration
4.urban to urban migration
On the basis of Geography:
1. Inter-regional migration
2. Intra-regional migration

Types of International Migration
On the basis of time:
1.Permanent Migration
2.Temporary migration (for less than 5 years stayed outside the country)

On the basis of interest or situation:
1. Forced Migration
2. Free Migration

On the basis of nature of migration
1.Legal Migration
2. Illegal migration
3.Refugees

Life Table

A life table is a concise way of showing the probabilities of a member of a particular population living to or dying at a particular age. In this study, the life tables are used to examine the mortality changes in the Social Security population over time.
Uses of Life Table:
1.Comparison of mortality
2.Estimation of life expectancy
3. Estimation of survival rate
4. Projection of Population
5.Study of stationary population

Population pyramid

A population pyramid is a graphical illustration that shows the distribution of various age groups in a population (typically that of a country or region of the world), which forms the shape of a pyramid when the population is growing. It is also used in ecology to determine the overall age distribution of a population; an indication of the reproductive capabilities and likelihood of the continuation of a species.

It typically consists of two back-to-back bar graphs, with the population plotted on the X-axis and age on the Y-axis, one showing the number of males and one showing females in a particular population in five-year age groups (also called cohorts). Males are conventionally shown on the left and females on the right, and they may be measured by raw number or as a percentage of the total population.

Population pyramids are often viewed as the most effective way to graphically depict the age and sex distribution of a population, partly because of the very clear image these pyramids present.

A great deal of information about the population broken down by age and sex can be read from a population pyramid, and this can shed light on the extent of development and other aspects of the population. A population pyramid also tells how many people of each age range live in the area. There tends to be more females than males in the older age groups, due to females' longer life expectancy.

Importance and Uses:

Population pyramids can be used to find the number of economic dependents being supported in a particular population. Economic dependents are defined as those under 15 (children who are in full-time education and therefore unable to work) and those over 65 (those who have the option of being retired). In some less developed countries children start work well before the age of 15, and in some developed countries it is common to not start work until 30 (like in the North European countries), and people may work beyond the age of 65, or retire early. Therefore, the definition provides an approximation. In many countries, the government plans the economy in such a way that the working population can support these dependents. This number can be further used to calculate the dependency ratio in that population.

Population pyramids can be used to observe the natural increase, birth, and death rate.

Marriage

Marriage is a social union or legal contract between spouses that establishes rights and obligations between them, between them and their children, and between them and their in-laws. It is the state of being united to a person of the opposite sex as husband or wife in a consensual and contractual relationship recognized by law.
According to Malinowski, "Marriage is a contract for the production and maintenance of children." According to Gillin and Gillin, "Marriage is a socially approved way of establishing a family of procreation." H. M. Jonson viewed, "Marriage is a stable relationship in which a man and a woman are socially permitted, without a loss of standing in community, to have children."
There are various types of marriages. They are classified into following types:
1. On the basis of number of marriage:
i.  Monogamy:
Monogamy, the most widespread form of marriage is found among the primitive as well as the civilized people. Monogamy is a form of marriage in which one man marries one woman. 
ii.  Polygamy:
Polygamy is a plural marriage including more than one spouse at the same time. It is also divided into two types: (1) Polyandry and (2) Polygyny. Polyandry is the marriage of one woman with several men. Polygyny is a form of marriage in which one man marries more than one woman at a time.

2. On the basis of marriage process:
 i. Arrange Marriage
 ii.  Love Marriage
 iii.  Court Marriage

3. On the basis of demographic view:
 i. Child MArriage (girls age below 16)
ii. Early Marriage: ( girls age 16-24 and boys age 25-30)
iii. Delayed Marriage (girls age above 25 and boys age above 30)

Marital Status:
A person's marital status indicates whether the person is married. According to UN marital status are divided into following types:
1. Single or Never Married
2.Married
3. Widowed
4. Divorced
5. Separated
6. Remarried

ERRORS IN DEMOGRAPHIC DATA

Despite the care taken to ensure the quality of the data collected by enumeration and registration, it will some time give obvious indications of errors in basic information. Usually errors in censuses and vital statistic registration (VSR) are of two types:

1.       Coverage.

2.       Content.

    A third type of error is sampling error which is introduced when sampling is used.

1.    ERROR OF COVERAGE:

                                        It is the common observation that a conduct or survey some households are missed and not counted, others may be counted two times. In VSR (vital statistic registration) there are cases which skip in registration (birth, date, marriages) these situation errors in demographic data offer must be made to cover all units and events of all observations which fall in our domain.

Coverage error are of two types:
1. Over enumeration
2. Under enumeration 

2.    ERRORS IN CONTENT:

                                      The term error of content refers to instance where the characteristic of a person counted in a census enumeration or in registration or in a survey are in correctly reported, recorded and tabulated or sometime they are completely missing.

                                      Besides from the errors due to carelessness or mistakes in judgment in a census or VSR, errors of coverage or content or both can arise at any step from initiation of an original record publication to the final tabulation or final record. The five principles are:

                                 i.            The respondent.

                               ii.            The recorder/ enumerator /investigator.

                              iii.            The coding process.

                             iv.            The editing process.

                               v.            Compiling and printing process.

                                                    The respondent error may be occur due to ignorance, illiteracy or will full wrong answer. For example: a person may not remember his/her correct age or he/she may will fully give wrong age or income etc. sometimes the respondent does not understand the question and give wrong information, this type of errors known as respondent error.

                                                   The second source of error is one part of enumerator who may not listen correctly or may made wrong entries. The errors at the stage of coding, editing and classification are quiet common. Placing of code at the right place is very much necessary. Editors have to give extra care in comparing logical answer of similar and related question. Similarly at the time of classification, tabulation and printing certain error do crept.

Content errors of two types;
1. Age misreporting
2. Recall lapse error

DETECTION OF ERRORS:

                                          In VSR errors may be detected by comparison of either tabulated data or individual records. Comparisons of tabulated data may yield or may be made either by internal comparison with previous census results or comparison with independent collateral data. Internal comparison may revealed inconsistency between related data in the tabulated result ratio to male or female for ages at some stages of life may appear to be out of line. Comparison can be made with previous census and vital statistics. For example: a census may shoe fewer or more persons in an age group than expected keeping in mind mortality and migration patterns.

         i.            COMPARISON WITH COLLATERAL DATA means to look at related independent data that is number of children in schools, number of buses, housing unit, electric meters etc.

       ii.            COMPARISON OF INDIVIDUAL RECORDS census return of individual is critically examined with reference to itself and some other co-lateral records’. Registration of individual tax return etc.

      iii.             RE-ENUMERATION SURVEY/ POST ENUMERATION SURVEY

        In order to check the quality of census returns a re-enumeration survey or post enumeration survey is conducted on selected units. This survey is conducted by senior professionals and all efforts are being made to obtain accurate records. Schedules of these surveys are than compared with census returns. To measure the error of content, the post enumeration survey is sometimes known as content evaluation survey (CES) and it is supposed to be accurate among all exercise.
 iv.    Cross check

Sample Survey

Sample survey is the process of collecting, compiling, evaluating and publishing demographic, social and economic data about the sample population at a specified time.
In statistics, survey sampling describes the process of selecting a sample of elements from a target population in order to conduct a survey. A survey may refer to many different types or techniques of observation, but in the context of survey sampling it most often involves a questionnaire used to measure the characteristics and/or attitudes of people. Different ways of contacting members of a sample once they have been selected is the subject of survey data collection. The purpose of sampling is to reduce the cost and/or the amount of work that it would take to survey the entire target population. A survey that measures the entire target population is called a census
 Objective and Scope:
The objectives of sample survey are as follows;
1. to predict the demographic variables
2, to fill the gap between two census
3. Takes less time and less economy
4. to get knowledge about birth, death, migration, family planning and employment
5.Represents the whole population

The scope of sample survey are as follows;
1. Birth, Death, marriage and its determining factors
2. The status and nature of birth and death
3. Health condition of child and mother
4. knowledge about HIV/AIDS and sexually transmitted diseases
5. Status of women
6. Status of employment and quality of life
7. socio-economic status of population

Types of demographic sample survey
1. Longitudinal Survey:
Longitudinal surveys are surveys that involve collecting data from multiple subjects on multiple occasions. They are typically used for collecting data relating to social, economic, educational and health-related issues and they serve as an important tool for economists, sociologists, and other researchers.
 2. Cross Sectional Survey
Cross-sectional survey form a class of research methods that involve observation of all of a population, or a representative subset, at one specific point in time. They differ from case-control studies in that they aim to provide data on the entire population under study, whereas case-control studies typically include only individuals with a specific characteristic, with a sample, often a tiny minority, of the rest of the population. 

Vital Registration

Vital registration are statistics on live births, deaths, fetal deaths, marriages and divorces. The most common way of collecting information on these events is through vital registration, an administrative system used by governments to record vital events which occur in their populations. Efforts to improve the quality of vital statistics will therefore be closely related to the development of vital registration systems in countries.
Vital registration, as defined by the United Nations, is the” continuous, permanent, compulsory, and universal recording of the occurrence and characteristics of vital events (livebirths, deaths, fetal deaths, marriages, and divorces) and other civil status events pertaining to the population as provided by decree, law or regulation, in accordance with the legal requirements in each country.”

There are many factors affecting the completeness of vital statistics in Nepal.
1. Lack of awareness to vital registration 
2. Organizational Problem
3. lack of trained and skilled full time personnel
4. Economic Problem
5. Adverse geographical condition
6. Administrative Problem

Uses of Vital Statistics
1. Vital Statistics is used for various purpose. It is used to analyse birth rate, death rate,marriage rate, rate of natural increase and population  dynamics.
2.  To lunch various programs like general health service, medical research, family planning.
3. It also helps to provide information needed for settlement, education, social security and insurance like administrative planning.
4. It keeps the record of important events of life so it is useful for verification of kins, relations with family, to take citizenship certificate, to admit children to schools etc.
5. to make various laws this statistics is used.

Limitations of Vital Statistics    1. Since vital registration is recorded for administrative purpose, it is difficult to get enough information about population studies.
2. Since all the life events are not  registered, it is not considered as the reliable medium.
3. Publication and use of vital statistics on time is not done, so it is not of any use.
4.Only by the study of vital statistics, all the population of the county cannot be determined.

Census and its Characteristics & Method pros n cons

A census is the procedure of systematically acquiring and recording information about the members of a given population. It is a regularly occurring and official count of a particular population.  The term is used mostly in connection with national population and housing censuses; other common censuses include agriculture, business, and traffic censuses. The United Nations defines the essential features of population and housing censuses as "individual enumeration, universality within a defined territory, simultaneity and defined periodicity", and recommends that population censuses be taken at least every 10 years. United Nations recommendations also cover census topics to be collected, official definitions, classifications and other useful information to coordinate international practice.

These censuses have four main characteristics:

• Universality: The census should cover the territory of the entire country, which ensures that all persons and all housing units are included. Sometimes, this goal is not achievable, for instance, if parts of a country experience conflict or if there are special population groups that are hard to enumerate, such as nomadic people. In those cases, a census may be complemented by statistical sampling.
• Individual enumeration: A census requires that each person or dwelling unit is enumerated individually so that their characteristics are captured separately. This facilitates cross-tabulation of census indicators and compilation of information for small areas.
• Simultaneity: A census is representative of the status at a specified time, usually a single day or a period of a few days in which the information is collected. Some questions, such as the birth or death of family members, refer to a longer reference period, such as the year before the census. A census is defined as de facto if it records persons according to their actual location at the time of enumeration or de jure if persons are referenced at their usual place of residence. This distinction can make a significant difference, for example, in countries with many temporary migrant workers.
• Defined periodicity: An important purpose of a census program is to provide information about changes over time. For instance, demographic projections tend to rely on information from two or more censuses. A census should therefore be conducted at regular intervals. Because of the large cost involved, most countries conduct censuses only every 10 years, although the periodicity is less regular in many developing countries.

Canvasser Method or Direct Interview Method of Census:

In this method, there are two method:

1. De facto Method

2. De jure Method:

(a) De facto methods: A de facto census is one that counts all persons as residents of the place they happen to be at the time the census is taken. In practice, de facto censuses are conducted in such a way that most people are counted in the places they usually live, but not always.

Advantage: Very clear and simple, international comparison are easy, the time taken is short and the information obtained is reliable.

Disadvantage: Floating population not counted, large number of trained and qualified personnel is required and mistakes occur because of rapid and fast method o f enumeration.

(b) De jure methods: When a de jure census is taken, there is always some uncertainty abut what should be considered a person's usual or normal place of residence.

Advantage: Due to availability of sufficient time, inaccuracies are reduced to the minimum, more questions can be asked, and the information obtained is dependable.

Disadvantage: Difficulty arises in the definition of temporary, and permanent, birth and death goes uncounted between the periods and it is difficult to count persons who have no permanent address.

Advantages of census

• provides a true measure of the population (no sampling error)
• benchmark data may be obtained for future studies
• detailed information about small sub-groups within the population is more likely to be available
• helps to make life table
• can predict the future population 

Disadvantages

• may be difficult to enumerate all units of the population within the available time
• higher costs, both in staff and monetary terms, than for a sample
• generally takes longer to collect, process, and release data than from a sample
• difficult to conduct census in war affected areas
• difficult to conduct due to geographical condition