Sampling Methods

1. Course: MBACourse: MBA
Subject: Research MethodologySubject: Research Methodology
Unit-3.3Unit-3.3
SAMPLING METHOD

2. • Sampling Concepts
• Methods
• Procedure
• Sample size decisions

3. What is Sampling?What is Sampling?
• the process of selecting a smallthe process of selecting a small
number of elements from a largernumber of elements from a larger
defined target group of elementsdefined target group of elements
• the information gathered from thethe information gathered from the
small group will allow judgments tosmall group will allow judgments to
be made about the larger groupsbe made about the larger groups

4. Why sampling?Why sampling?
• Inability to analyze large quantities ofInability to analyze large quantities of
data potentially generated by adata potentially generated by a
populationpopulation
• Practical considerations such as costPractical considerations such as cost
and timeand time
• Sampling can produce sound results ifSampling can produce sound results if
proper rules are followed for the drawproper rules are followed for the draw

5. Basic concepts of SamplingBasic concepts of Sampling
• PopulationPopulation
• SampleSample
• Sampling unitSampling unit
• Sampling errorSampling error
• Sampling frameSampling frame
• Sampling sizeSampling size

6. Basic concepts of SamplingBasic concepts of Sampling
• Population:Population: baseline -baseline -thethe
entire group under studyentire group under study
as defined by objectivesas defined by objectives
• Sample:Sample: a subset of thea subset of the
population that shouldpopulation that should
represent the entirerepresent the entire
groupgroup

7. Basic concepts of SamplingBasic concepts of Sampling
• Sample unit:Sample unit: the basic level of investigationthe basic level of investigation
• Sampling error:Sampling error:
same sampling methods, same population, the studysame sampling methods, same population, the study
with a larger sample size will have less sampling processwith a larger sample size will have less sampling process
error compared to the study with smaller sample sizeerror compared to the study with smaller sample size

8. Basic concepts of SamplingBasic concepts of Sampling
• Sampling frame:Sampling frame:
a master list of thea master list of the
population (total or partial)population (total or partial)
from which the sample willfrom which the sample will
be drawnbe drawn
• Sampling size:Sampling size: number ofnumber of
samples to be drawnsamples to be drawn

9. Types of SamplingTypes of Sampling
• Probability samplingProbability sampling
in which members ofin which members of
the population have athe population have a
known chanceknown chance
(probability) of being(probability) of being
selectedselected
• Non-probabilityNon-probability
samplingsampling
in which the chancesin which the chances
(probability) of selecting(probability) of selecting
members from themembers from the
population arepopulation are
unknownunknown

10. Sampling methodsSampling methods
ProbabilityProbability
• Simple randomSimple random
samplingsampling
• Stratified randomStratified random
samplingsampling
• Systematic samplingSystematic sampling
• Cluster samplingCluster sampling
Non-probabilityNon-probability
• Convenience samplingConvenience sampling
• Judgment samplingJudgment sampling
• Quota samplingQuota sampling
• Snowball samplingSnowball sampling

11. Probability Sampling MethodsProbability Sampling Methods
Simple random methodSimple random method
every unit has an equal non-zeroevery unit has an equal non-zero
chance of being selectedchance of being selected
• Advantages:Advantages:
– Known and equal chance ofKnown and equal chance of
selectionselection
– Easy method when there isEasy method when there is
an electronic databasean electronic database
• Disadvantages:Disadvantages:
– Complete accounting ofComplete accounting of
population neededpopulation needed
This method is the purest form of probability sampling

12. Probability Sampling MethodsProbability Sampling Methods
Stratified randomStratified random
methodmethod
the population is separatedthe population is separated
into homogeneous strata and ainto homogeneous strata and a
sample is taken from eachsample is taken from each
• Advantages:Advantages:
– More accurate overallMore accurate overall
sample of skewedsample of skewed
populationpopulation
• Disadvantages:Disadvantages:
– More complex samplingMore complex sampling
plan requiring differentplan requiring different
sample sizes for eachsample sizes for each
stratumstratum
Often used when one or more of the stratums in the population
have a low incidence relative to the other stratums.

13. Probability Sampling MethodsProbability Sampling Methods
Systematic methodSystematic method
the defined target population isthe defined target population is
ordered and the sample isordered and the sample is
selected according to positionselected according to position
using a skip intervalusing a skip interval
• Advantages:Advantages:
– Known and equal chance ofKnown and equal chance of
selected intervalselected interval
– Less expensive…faster thanLess expensive…faster than
Radom methodsRadom methods
• Disadvantages:Disadvantages:
– Loss in sampling precisionLoss in sampling precision
Systematic sampling is frequently used to select a specified
number of records from a computer file.

14. Probability Sampling MethodsProbability Sampling Methods
Cluster methodCluster method
the population is divided intothe population is divided into
groups (clusters), any of whichgroups (clusters), any of which
can be considered acan be considered a
representative samplerepresentative sample
• Advantages:Advantages:
– Economic efficiency …Economic efficiency …
faster and less expensivefaster and less expensive
– Does not require a list of allDoes not require a list of all
members of the populationmembers of the population
• Disadvantages:Disadvantages:
– Cluster specification error…Cluster specification error…
the more homogeneous thethe more homogeneous the
cluster chosen, the morecluster chosen, the more
imprecise the sample resultsimprecise the sample results

15. Non-probability Sampling MethodsNon-probability Sampling Methods
ConvenienceConvenience
sampling methodsampling method
the selecting on the basis ofthe selecting on the basis of
convenienceconvenience
the selection at familiarthe selection at familiar
locations and to chooselocations and to choose
respondents who are likerespondents who are like
themselvesthemselves
Judgment methodJudgment method
selecting samples that requireselecting samples that require
a judgment or an “educateda judgment or an “educated
guess”guess”
often used during preliminary research efforts to get a gross
estimate of the results
must be confident that the chosen sample is truly
representative of the entire population.

16. Non-probability Sampling MethodsNon-probability Sampling Methods
Quota sampling methodQuota sampling method
samples that set a specificsamples that set a specific
number of certain types ofnumber of certain types of
individualsindividuals
Often used to ensure desiredOften used to ensure desired
proportion of differentproportion of different
respondent classesrespondent classes
Snowball methodSnowball method
selecting samples whichselecting samples which
require respondents to providerequire respondents to provide
the names of additionalthe names of additional
respondentsrespondents
special method used when the desired sample characteristic is
rare

17. Online Sampling Techniques
• Random online intercept sampling:Random online intercept sampling:
relies on a random selection of Web site visitorsrelies on a random selection of Web site visitors
• Invitation online sampling:Invitation online sampling:
is when potential respondents are alerted that they may fillis when potential respondents are alerted that they may fill
out a questionnaire that is hosted at a specific Web siteout a questionnaire that is hosted at a specific Web site
• Online panel sampling:Online panel sampling:
refers to consumer or other respondent panels that are setrefers to consumer or other respondent panels that are set
up by marketing research companies for the explicit purposeup by marketing research companies for the explicit purpose
of conducting online surveys with representative samplesof conducting online surveys with representative samples

18. Developing a SamplingDeveloping a Sampling
PlanPlan
• Step-1Step-1
Define the relevantDefine the relevant
population (baseline)population (baseline)
• Step-2Step-2
Identify sample frameIdentify sample frame
• Step-3Step-3
Determine specific samplingDetermine specific sampling
method, all necessary stepsmethod, all necessary steps
must be specifiedmust be specified
• Step-4Step-4
Determine sample size,Determine sample size,
selecting samplesselecting samples
• Step-5Step-5
Execute the samplingExecute the sampling
• Step-6Step-6
SSampling validationampling validation
--compare sample profilecompare sample profile
with population profile Re-with population profile Re-
sampling if necessarysampling if necessary

19. Factors to consider in sampling design
• Work objectivesWork objectives
• Degree of accuracyDegree of accuracy
• ResourcesResources
• Time frameTime frame
• Knowledge on populationKnowledge on population
• ScopeScope
• Statistical analysis needsStatistical analysis needs

20. How to determine sample size?

21. Common approaches for determining
sample size
– Budget/time available
– Executive decision
– Statistical methods
– Historical data/guidelines
ISBN: 8173196257

22. ConclusionsConclusions
• A well-designed sampling plan answers the
following questions –
What will be learned?
How long will it take?
How much will it cost?
Sampling is important for a survey/research projectSampling is important for a survey/research project
Many sampling start with a general hope that somethingMany sampling start with a general hope that something
interesting will emerge, and often end in frustrationinteresting will emerge, and often end in frustration

23. Reference
• http://www.surveysampling.com/
http://www.surveysystem.com/