Sampling technqiues

CENSUS VS. SAMPLING
CENSUS
• Census refers to a periodic
collection of information about the
populace from the entire
population.
SAMPLE
• Sampling is a method of collecting
information from a sample that is
representative of the entire
population.
3
Dr.M.Jothilakshmi, VVVCollege, Virudhunagar

RELIABILITY
CONTENT CENSUS SAMPLE
Reliability Data from the census is
reliable and accurate.
There is a margin of error
in data obtained from
sampling.
Time Census is very time-
consuming.
Sampling is quick.
Cost Census is very
expensive
Sampling is inexpensive.
Convenience It is not very convenient
as the researcher has to
allocate a lot of effort in
collecting data.
Sampling is the most
convenient method of
obtaining data about the
population.
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5

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• Population: The aggregate of all the units pertaining to a
study. It is called as universe or target population.
• All the teaching professionals in VNR – A study on stress
management
• Element: A member of population.
• Individual staff members
• Sample: A subset of units in a population, selected to
represent all units in a population of interest.
• A list of professors who respond to the study.
• Sample unit: Element or set of elements considered for
selection in some stage of sampling.
• College wise classification, Discipline wise classification 7

• Sample frame: This is the actual list of sampling units
from which the sample, or some stage of the sample, is
selected. It is simply a list of the study population.
• Telephone directory, College address book.
• Sample design: A set of rules or procedures that specify
how a sample is to be selected. This can either be
probability or non-probability.
• Using a convenience sampling method to select the
sample professors
• Sampling: A process od drawing a sample from population.
• Sample size: The number of elements in the obtained
sample.
• 1500 college professors
8

SAMPLING
METHODS/TECHNIQUES
Probability
Non-
Probability
9

PROBABILITY/RANDO
M
• SIMPLE RANDOM
• STRATIFIED
• SYSTEMATIC
• CLUSTER
• AREA
• MULTI-STAGE & SUB
SAMPLING
• MULTI PHASE & DOUBLE
• REPLICATED
NON-
PROBABILITY/NON-
RANDOM
• CONVENIENCE
• PURPOSIVE
• QUOTA
• SNOW BALL SAMPLING
10

SIMPLE RANDOM SAMPLING
Every member of the population has an equal chance
of selection.
11Dr.M.Jothilakshmi, VVVCollege, Virudhunagar

Lottery Method
Sampling with
replacement/
Unrestricted random
sampling
Sampling without
replacement/
Restricted
sampling
13

• Heterogeneous population is divided into exclusive homogeneous group
& sample are drawn from each group.
• Each homogeneous group is called as “Strata”.
• Collection of strata is referred as “Stratum”
STRATIFIED SAMPLING
Students
College
Arts &
Science
Technical
School
Primary
Secondary
15

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Draw a sample from each stratum

SYSTEMATIC RANDOM SAMPLING
• Procedure:
• The first unit is selected at random from the sample frame.
• Other units selected at the regular intervals depending on the
size on the sample frame.
• It is known as “Fixed Interval method”.
• As it having the nonprobability traits, it is referred as “
Pseudo-random sampling”.
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Systematic sampling
19

SYSTEMATIC SAMPLE
• EVERY KTH MEMBER ( FOR EXAMPLE: EVERY 10TH
PERSON) IS SELECTED FROM A LIST OF ALL POPULATION
MEMBERS.
Math
Alliance
Project
20

CLUSTER SAMPLING
Section 4
Section 5
Section 3
Section 2Section 1
21

• A probability sampling method in which items are
chosen in clusters rather than individually from the
population is called “cluster sampling”.
• The clusters are termed as “Primary Units”.
• Random choice for selecting elements is two stages
is called as “Two stage cluster sample”.
22

Area Sampling
A method of sampling when no complete frame of
reference is available. The total area under
investigation is divided into small sub-areas which
are sampled at random or by some restricted random
process.
23

MULTISTAGE SAMPLING
• Multistage sampling can be a complex form of cluster sampling.
Dividing the population into groups (or clusters) then, one or more
clusters are chosen at random and everyone within the chosen cluster
is sampled.
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DOUBLE AND MULTI PHASE
SAMPLING
• A sampling method in which certain items of
information are drawn from the whole units of a
sample and certain other items of information are
taken from the subsample.
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Convenience sampling
• The researcher selects the most accessible population members from which
to get information.
• Sample which are very close to hand, very convenient, readily available or
willing to respond are chosen.
• It is called as “Grab/ Opportunity Sampling/Accidental sampling”
• “Collecting data from friends, acquaintances or from
colleagues”
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JUDGEMENT SAMPLING
• The researcher uses judgement to select population
members who are good prospects for accurate
information.
• It known as “purposive of authoritative sampling”
• Collecting details regarding VVV MBA from the
students from corresponding dept.
31

QUOTA SAMPLING
• The researcher finds and collect data from a
prescribed number of people in each of several
categories.
• Out of 100 respondents, select 50 from school, 50
from college.
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SNOW BALL SAMPLING
• “Chain sampling, chain-referral sampling or
referral sampling”.
• A snowball sample is one in which the researcher
collects data on the few members of the target
population he or she can locate, then asks those
individuals to provide information needed to
locate other members of that population whom
they know.
• A study on homeless, requires very few people
and they would lead to reach others. 33

•
Linear
Exponential
Non-Discriminative
Exponential
Discriminative34

Sampling technqiues

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