Research Methodology - Introduction
Steps In Sampling Design
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A researcher should take into consideration the following aspects while developing a sample design:
Steps In Sampling Design:
A researcher should take into consideration the following aspects while developing a sample design:
The first step involved in developing sample design is
to clearly define the number of cases, technically known as the universe. A
universe may be finite or infinite. In a finite universe the number of items is
certain, whereas in the case of an infinite universe the number of items is
infinite (i.e., there is no idea about the total number of items). For example,
while the population of a city or the number of workers in a factory comprise finite
universes, the number of stars in the sky, or throwing of a dice represent
infinite universe.
Prior to selecting a sample, decision has to be made
about the sampling unit. A sampling unit may be a geographical area like a
state, district, village, etc., or a social unit like a family, religious
community, school, etc., or it may also be an individual. At times, the
researcher would have to choose one or more of such units for his/her study.
Source list is also known as the ‘sampling frame’,
from which the sample is to be selected. The source list consists of names of
all the items of a universe. The researcher has to prepare a source list when
it is not available. The source list must be reliable, comprehensive, correct,
and appropriate. It is important that the source list should be as
representative of the population as possible.
Size of the sample refers to the
number of items to be chosen from the universe to form a sample. For a
researcher, this constitutes a major problem. The size of sample must be
optimum. An optimum sample may be defined as the one that satisfies the
requirements of representativeness, flexibility, efficiency, and reliability.
While deciding the size of sample, a researcher should determine the desired
precision and the acceptable confidence level for the estimate. The size of the
population variance should be considered, because in the case of a larger
variance generally a larger
sample is required. The size of the population should be considered, as it also limits the sample size. The parameters of
interest in a research study should also be considered, while deciding the
sample size. Besides, costs or budgetary constraint also plays a crucial role
in deciding the sample size.
The specific population parameters of interest should also be considered while determining the sample design. For example, the researcher may want to make an estimate of the proportion of persons with certain characteristic in the population, or may be interested in knowing some average regarding the population. The population may also consist of important sub-groups about whom the researcher would like to make estimates. All such factors have strong impact on the sample design the researcher selects.
From the practical point of view, cost considerations exercise a major influence on the decisions related to not only the sample size, but also on the type of sample selected. Thus, budgetary constraint could also lead to the adoption of a non-probability sample design.
Finally, the researcher should decide the type of sample or the technique to be adopted for selecting the items for a sample. This technique or procedure itself may represent the sample design. There are different sample designs from which a researcher should select one for his/her study. It is clear that the researcher should select that design which, for a given sample size and budget constraint, involves a smaller error.
A researcher should take into consideration the following aspects while developing a sample design:
Type Of Universe:
Sampling Unit:
Source List:
Size Of Sample:
(A) Parameters Of Interest:
The specific population parameters of interest should also be considered while determining the sample design. For example, the researcher may want to make an estimate of the proportion of persons with certain characteristic in the population, or may be interested in knowing some average regarding the population. The population may also consist of important sub-groups about whom the researcher would like to make estimates. All such factors have strong impact on the sample design the researcher selects.
(B) Budgetary Constraint:
From the practical point of view, cost considerations exercise a major influence on the decisions related to not only the sample size, but also on the type of sample selected. Thus, budgetary constraint could also lead to the adoption of a non-probability sample design.
(c) Sampling Procedure:
Finally, the researcher should decide the type of sample or the technique to be adopted for selecting the items for a sample. This technique or procedure itself may represent the sample design. There are different sample designs from which a researcher should select one for his/her study. It is clear that the researcher should select that design which, for a given sample size and budget constraint, involves a smaller error.
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