Sampling techniques.pptx

Sampling Techniques
Types
Probability sampling
Non probability sampling
Errors

 Sampling techniques is process or technique
of selecting a sample of appropriate
chracteristic and adequate size.
 The main OBJECTIVES OF SAMPLING are :
1) Estimation of population PARAMETERS
from sample STATISTICS.
2) To TEST THE HYPOTHESIS about population
from which the sample or samples are
drawn.

Sampling
Non-
Probability
Sampling
Convenience
Quota
Judgement
Probability
Sampling
Simple
Random
Systematic
Stratified
Cluster

 Applicable when the population is
small,homogeneous and readily available
 Principle is that every member or every unit
of the population has an equal chance of
being selected
 Unrestricted Random sampling
 Two Methods
1) Lottery Method
2) Table of Random Number Method

 Used in those cases where a complete list of
population from which sample is to be drawn
is available.
 More often applied to field studies where
population is large, scattered and
homogeneous.
Choose every Kth house where ‘K’ refers to
the SAMPLING INTERVAL

 Used when the population is not
homogeneous so population is divided into
different subgroups and samples are selected
from each.
 The population under study is first divided
into homogeneous groups or classes called
‘strata’ & sample is drawn from each stratum
at random in proportion to its size
 Then samples from each stratum is combined
to form a single sample.

 Population is heterogeneous, vast and
scattered over vast area.
 First stage a sample of areas is chosen
 Second stage a sample of respondents within
those areas is selected.
 Population divided into clusters of
homogeneous units, usually based on
geographical contiguity.
 A sample of such clusters is then selected, all
units of selected cluster is studied.

 The first stage is to select the groups or
clusters. Then subsamples are taken in as
many subsequent stages as necessary to
obtain the desired sample size
 1st stage: Choice of states within countries
 2nd stage: Choice of towns within eachstate
 3rd stage: Choice of neighborhoods within
each town

 Prone to bias
 Allows estimation of magnitude of sampling
error, from which you can determine the
statistical significance of
changes/differences in indicators

• Requires that you have a list of all sample
elements
• More time-consuming
• More costly
• No advantage when small numbers of
elements are to be chosen

1. Convenience sampling:-
 Selection is made from an available source
like that from a nearby resources for ease of
convenience
 Example: coworkers, students from nearby
college, mall
 Non-random sampling method gives less
precise result compared to random sampling
method, but time, cost and resource
required will be considerably less

2.Judgmental sampling:
The researcher chooses the sample based on who
they think would be appropriate for the study.
This is used primarily when there is a limited
number of people that have expertise in the area
being researched
3. Quota sampling:there are two types of quota
sampling:
Proportional: In proportional quota sampling you
want to represent the major characteristics of
the population by sampling a proportional
amount of each.
Non proportional: Non proportional quota
sampling is a bit less restrictive. the minimum
number of sampled units is specified in each
category. not concerned with having numbers
that match the proportions in the population

 More flexibleLess costly
 Less time-consuming
 Judgmentally representative samples may be
preferred when small numbers of elements
are to be chosen

 Greater risk of bias
 May not be possible to generalize to program
target population
 Subjectivity can make it difficult to measure
changes in indicators overtime
 No way to assess precision or reliability of
data

1.Sampling error: If we take the sample from
the same population, whatever the care has
been taken to choose the sample the results
will differ from sample to sample.
 The occurrence of this variation from one
sample to another sample is called sampling
error.
 It may occur due to faulty sample design or
due to small size of sample

2.Non-sampling Error (systematic
error)
Errors that occur due to
1.inadequately calibrated
Instruments
2.observer variation
3.incomplete coverage achieved in
examining the subjects selected and
conceptual sampling errors.

Sampling techniques.pptx

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