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government can make special arrangement in health sector. Similarly, it is helpful to know
about economically active population, old people above 60 years from citizenship records
and voters list. The government can adopt economic plan and policy from such data.
The records of passport issues by government bodies can support government to guess
foreign visit or migration of people.

iv. Sample survey

Sample survey is the method of collecting information on population by taking some
families or group of people as a sample. In this method, questionnaires are prepared
and distributed among the samples. Later on, data are collected, analyzed, evaluated and
finally generalized for the entire population.
Sample survey was first started in Britain in 19 century. In Afghanistan, direct census
th
cannot be conducted. So, sample survey is used to collect information about population
in Afghanistan nowadays. In the context of Nepal, sample survey was conducted first in
1966 AD as the health survey. However, it was used to collect population data in 1974/75
A.D. 1975/76 A.D. and 1977/78 A.D.
Sample survey is regarded as mini census. When we have to conduct special research and
necessary data are not collected in census, sample survey can be used. It is not expensive
and easy to use. Less manpower can collect detail and quality information as they can spend
more time in interview. However, sample survey presents data of limited people which
may not reflect the exact information of entire population while generalizing it. Similarly,
there are chances of collecting inaccurate data if the enumerators are not well trained.

2.3 Determinants of Population Change
Those factors which determine the population and are responsible for change of
population are called determinants of population change. Birth, death and migration
are the determinants of population change. These all affect the population in a place.
Actually, population never remains constant in a place. It keeps on changing time and
again. Sometimes, the population is increased in a place and sometimes, it is decreased.
Birth and death take place very often in a place. People keep on migrating from place to
place as well.
Birth and death are natural factors of population change. People have no control over
birth. Though the gestation period in human beings lasts for 9 months, we cannot exactly
say about the time of birth of the child. Once a person is born, no one is immortal in the
world. Sooner or later, everyone has to die. But we cannot say when will a person die.
Death is not in our hand. Migration is the artificial factor of population change. People
migrate from place to place due to several reasons. It depends upon individual wish
whether to change a place or not.
We can explain the determinants of population change by means of flow model of
population change.

GREEN Environment Population and Health Education Book-9 29