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SAMPLING
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Contents….
Meaning of sampling
Characteristics of sample
Why sampling
Sampling techniques or methods
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Meaning ;
Sampling means obtaining information from a portion of a larger
group or from universe.
Elements are selected in a manner that they yield all most all
information about the whole universe, if and when selected
according to some scientific principles and procedures.
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Definition of Sample;
Ya – Lun – Chou defines a sample “ as a collection
of primary sampling units, select as a representative
microcosm, from which references about the
population may be made.”
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Characteristics of Good Sample
Representativeness
Accuracy
Precision
Size
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Why Sampling???
Advantages of Sampling
Sampling reduces the time and cost of
research studies.
Sampling saves labour.
Sampling helps to collect vital information
more quickly.
Sampling is easier.
Accuracy is concerned in sampling
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Disadvantages of Sampling
It demands a thorough knowledge of sampling
methods and procedures.
It is not feasible.
Sampling procedures must be correctly designed
and followed.
Reliability depends up on the representativeness of
the sample.
It requires service of sampling experts or
statisticians.
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Sampling Techniques or Methods
Sampling techniques or methods may be classified
in two generic types:-
1. Probability or Random Sampling
2. Non Probability or Non Random Sampling
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SAMPLING METHODS
Probability SamplingNon – Probability Sampling
Simple Designs
Simple Random Sampling
Stratified Random Sampling
Systematic Random Sampling
Complex Design
Cluster and Area Sampling
Multi Stage and Sub Sampling
Double Sampling and multi Face
Sampling
Replicated Sampling
Convenience or Accidental
Sampling
Purposive or Judgment
Sampling
Quota Sampling
Snow Ball Sampling
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Probability Sampling Techniques
Based on the theory of probability.
Every population has a chance of being selected.
Such a chance is a probability.
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Non – Probability Sampling
It does not ensure a selection chance to each
population unit.
The selection probability is unknown.
It may not be a representative one.
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Types of Probability Sampling
1. Simple Random Sampling
This type of sampling gives all units of the target
population an equal chance of being selected.
The sample units are selected by means of a
number of methods.
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Random Sampling Procedure
The Lottery Method
The Random Numbers Method
The Computer Method
Grid Method
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Advantages of Random Sampling
It is the easiest method.
All elements have an equal chance of being selected.
Sampling errors can be easily computed.
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Disadvantages
It is often impractical
It is time consuming
Units are arranged in specific order
It is difficult in the case of field surveys
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2. Stratified Random Sampling
This is a special form of simple random sampling
The population is divided in to a number of strata
The division of population is based on one or more
criteria.
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Steps in Stratified Random Sampling
Target population is divided into a number of strata
Sampling frames for each groups are identified
Drawing sample from each group
The sub samples are merged in to one sample
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Types of Stratified Random Sampling
Proportionate Stratified Sampling
Disproportionate stratified Random Sampling
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Proportionate Stratified Sampling
It is a very popular method
Drawing a sample from each stratum
It gives proper representation to each stratum
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Advantages
Proper representation to all sub groups
Higher statistical efficiency
It is easy to carry out
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Disadvantages
A prior knowledge is required
It is very expensive
Sometimes it lead to classification errors
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Disproportionate Stratified Random Sampling
It does not give proportionate representation to
strata
Over representation and under representation are
in this method.
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Advantages
It is less time consuming
It gives weightage to particular group
Disadvantages
Proportionate representation is not given to each
stratum
It requires a prior knowledge
It is subject to classification errors
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Systematic Sampling or Fixed Interval Method
It is an alternative to random sampling
Selection of sample units is dependent on the
selection of a previous one
It is sometimes called a “ pseudo – random “
sampling
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Advantages
It is much simple than random sampling
It is useful to field investigations
It requires less time
It is cheaper than simple random sampling
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Disadvantages
It cannot be considered to be a probability
sampling
Each element do not have an equal chance of
being selected
Sometimes it gives a biased sample
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Conclusion Sampling is one of the most fundamental elements of
research, and one that has attracted the interest of
many social researchers and alike.
Sampling is the method of choosing the respondents of
a study and one which is widely used in social research.
Some form of sampling is employed by quantitative and
qualitative researchers, although to a different extent
and in a different form.
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References;
1.Introduction to Research Methods in Social
Sciences
– K. Ravichandaran and S. Nakkiran
2.Social Research
– Sotirios Sarantakos
3.Methodology of Research in Social Science
– O. R. Krishnaswamy and M. Ranganatham