Population change refers to the difference between the size population at the beginning and at the end of a period.

It can refer to the growth or decline in population.

Population change can also be described as population growth.

This is the increase (positive growth) or decrease (negative growth) in the number of people.

Change in the population is caused by birth, death, and migration.


The factors influencing population change include the birth rate, death rate, and migration. These influence population change negatively and positively.


A high birth rate coupled with a low death rate results in a positive change in population.

This translates into an increase in population. A high birth rate is caused by high fertility and fecundity within a population. Fertility is defined as the ability to conceive or to reproduce.

Fecundity refers to the ability to give birth to many children’s i.e. high fertility. The fertility rate is expressed as a ratio of live birth in an area to the population of that area.

For example, according to the United Nations estimates for 1995  – 2000, the total fertility for Tanzania was 5.5 children per woman aged between 15 and 49 years.

This is the average number of children that women of child-bearing age will have in their lifetime.

The factors influencing fertility include the level of education of the women, urbanization, career prospects, and birth control measures.

These factors tend to influence the fertility rate.

The high fertility rate in East Africa is attributed to improved nutrition, improved health services, and the weakening of the traditional customs like a prolonged period of breastfeeding and sexual abstinence after birth.

The Crude Birth Rate (CBR)

The crude birth rate is estimated rate of births in a year.

It is not a precise figure because the values for the total population that are used for the calculation are an estimated by the middle of the year.

It is obtained by dividing the total number of birth recorded in the year by the estimated total population by the mid-year and multiplying the fraction by 1,000.

The formula would be the Total number of births in the year x 1,000 Total population (mid-year estimates) Tanzania crude birth rate during the period 1995 to 2000 was 40.2 annual live births per 1000 persons.


This factor is sometimes expressed as mortality and it refers to the number of deaths within a given population.

There are three (3) types of death rates. Infant Mortality Rate. Is the number of deaths in the first year of life per one thousand live births.

Child Mortality Rate. Is the number of deaths of children aged between 1 and 5 years per one thousand live births.

Adult Mortality Rate. Refers to the number of adults dying per one thousand of the total population. Mortality is significant in that it results in a reduction of population numbers. It also affects the population structure.

A high death rate of a particular sex or age has a negative bearing on population growth.

Large-scale mortality may be caused by an outbreak of war, famine, disease epidemic or natural disasters such as floods, earthquakes, and volcanic eruptions.

The deaths of a large number of youths and men who are of child-bearing age reduce the number of people involved in child-bearing. The Crude Death Rate (CDR)

The crude death rate is the estimated rate of deaths against an estimated total population by the middle of the year in question.

It is calculated in the same way as the crude birth rate, Thus: Total number of deaths rate in the year x 1000 Total population (mid-year estimate)

The crude death rate is also expressed as the number of deaths per one thousand people.

From the United Nations statistics, Tanzania’s crude death rate from 1995 to 2000 was 12.9 annual death per 1,000 persons.

The reason why they use the term “Crude” is that other characteristics such as age, sex, and composition within a population are ignored.

The natural population growth is obtained by subtracting the CDR from the CBR.

It can be expressed as percentages as

CBR-CDR  X 100 1000 From the 2002 population census conducted in Tanzania, the annual growth rate was found to be 2.9% for the period between 1988 and 2002 (i.e intercensal period).


Migration is the movement of people from one place or region to another which results in a change of residence.

It may be temporary or permanent. Migration may involve immigration where people come into a new area. Those people are referred to as immigrants.

It may also involve emigration where people leave their native land for another land. These people are called emigrants. Migration across countries’ borders is called International Migration.

Migration across the boundary within a country is called Internal Migration. Such migration influences population change on both sides (Origin and Destination) which are affected positively or negatively.

Emigration of a large number of people from their native land results in a reduction of population.

In Africa, an exodus of people from their native countries has largely been attributed to civil wars.

Large numbers of refugees flock to neighboring countries result in an increase in population in the host countries.

Tanzania has been host to many refugees from Rwanda, Burundi, Uganda, the Democratic Republic of Congo and even Somalia Migration of these refugees has resulted in a decrease in population in their native countries.

Some of the refugees may even opt to stay permanently in their host countries and some even change their citizenship.

The populations of refugees also grow through children born among them within the host countries. All these result in positive change in population.


There are two (2) types of migration which include internal migration and external (International) migration.

These types of migration can be in a form of permanent, temporary, voluntary, or involuntary.


This is a movement of people within a country. It can be temporary or long-term. It may be voluntary or forced.

This type of migration goes on all the time and many governments do not attempt to control it.

The reasons for this type of migration are varied. They include searching for jobs, settlement, seeking safer areas, or improvement of people’s lives.

There are those who move to parts of countries where the climate is more favorable. There are four (4) forms of internal migration

  1. Rural to Urban migration. In this form, people move from rural areas to towns. People migrate in search of jobs, better social amenities or education, some move to avoid wide spread of unemployment in the rural areas or work on farms.
  2. Rural to rural migration. In this form, people move from one rural area to another. Some people move into plantations for employment in the large farms. There are those who moved into new settlement and do farming.

Nomadic pastoralists migrate in search of water and pasture for their animals.

  1. Urban to rural migration. Some migrants who moved to towns in search of jobs move back to rural areas to settle because they now have capital to invest in the rural areas.
  2. Urban to urban migration. Are migrants who may move from one town to another. This may in search of better employment or business opportunities.


External migration is also known as international, interstate, or inter-regional migration. It is the movement of people from their own countries to other countries.

The people involved are referred to as in their original countries, emigrants, and as Immigrants in their destination countries. Migration may be voluntary as in the case where people go for further studies, employment, or settlement or it may be forced as in the case of refugees.

This migration can be temporary or permanent. For example, International tourists are temporary migrants.


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