introduction and the types of the sampling , advantages of the sampling and disadvantages of sampling

1. 1
SAMPLING
 OutlinesSampledefinition
 Purpose of sampling
 Stagesinthe selectionof asample
 Typesof samplinginquantitative researches
 Typesof samplinginqualitativeresearches
 Ethical ConsiderationsinDataCollection
The processof selectinga numberof individualsfor a study in such a way that the individualsrepresentthe larger
group from which theywere selected .
SAMPLING
TARGET POPULATION
STUDY POPULATION
SAMPLE
 A sample is“a smaller(buthopefullyrepresentative) collectionof unitsfromapopulationusedtodetermine
truthsabout that population”(Field,2005)
 The sampling frame
A listof all elementsorotherunitscontainingthe elementsinapopulation.
Population…
…the larger groupfromwhichindividualsare selectedtoparticipate inastudy.
Target population A setof elementslargerthanordifferent fromthe populationsampledandtowhichthe researcher
wouldlike togeneralize studyfindings.
The Purpose of Sampling……..
 To gather data aboutthe populationinordertomake an inference thatcanbe generalizedtothe population.
Stages in the selectionofa sample
1. Define the targetpopulation
2. Selectasamplingframe
3. Conductfieldwork
4. Determine if aprobabilityornonprobabilitysamplingmethodwill be chosen
5. Planprocedure forselectingsamplingunits
6. Determine samplesize

2. 2
7. Selectactual samplingunits
8. Conductfieldwork
Quantitative Sampling
 Purpose – to identifyparticipantsfrom whomtoseeksome information
 Issues◦ Nature of the sample (randomsamples)
◦ Size of the sample
◦ Methodof selectingthe sample
 Importantissues
◦ Representation –the extenttowhichthe sample isrepresentativeof the population
◦ Generalization –the extenttowhichthe resultsof the studycan be reasonablyextendedfromthe sample to
the population
◦ Samplingerror The chance occurrence that a randomly selected sample is not representative of the population due to
errors inherent in the sampling technique
◦ Samplingbias
Some aspectof the researcher’ssamplingdesigncreatesbiasinthe data.
◦ Three fundamentalsteps
1. Identifyapopulation
2. Define the sample size
3. Selectthe sample
Types ofsmpling inQuantitive Researchs
1. Probabilitysamples
2. Nonprobabilitysamples
SelectingRandom sample
 Knownas probabilitysampling
 Bestmethodto achieve arepresentative sample
 Four techniques
1. Random2. Stratifiedrandom3.Cluster4. Systematic
1. Random samplingSelectingsubjectssothatall membersof a populationhave anequal andindependentchance of
beingselected
Advantages 1. Easy to conduct
2. High probabilityof achievingarepresentative sample
3. Meets assumptionsof manystatistical procedures
Disadvantages 1. Identificationof all membersof the populationcanbe difficult
2. Contactingall membersof the sample canbe difficult
◦ Selectionprocess
1. Identifyand define the population
2. Determine the desiredsample size
3. List all membersof the population
4. Assignall memberson the listaconsecutive number
5. Selectanarbitrary startingpointfroma table of random numbersandreadthe appropriate numberof digits
Stratifiedrandom sampling ◦ The populationisdividedintotwoormore groups calledstrata,accordingto some
criterion,suchas geographiclocation,grade level,age,orincome,andsubsamplesare randomlyselectedfromeach
strata.
◦ Advantages

3. 3
1. More accurate sample
2. Can be usedfor bothproportional andnonproportional samples
3. Representationof subgroupsinthe sample
◦ Disadvantages
1. Identificationof all membersof the populationcanbe difficult
2. Identifyingmembersof all subgroupscanbe difficult
◦ Selectionprocess
1. Identifyanddefine the population
2. Determine the desiredsample size
3. Identifythe variableandsubgroups(i.e.,strata) forwhichyouwantto guarantee appropriate representation
4. Classifyall membersof the populationasmembersof one of the identifiedsubgroups
Clustersampling
 The processof randomlyselectingintactgroups,not individuals,withinthe definedpopulationsharingsimilar
characteristics
 Clustersare locationswithinwhichanintactgroup of membersof the populationcanbe found
a. Neighborhood
b. School districts
c. Schools
d. Classrooms
◦ Advantages
1. Very useful whenpopulationsare large andspreadovera large geographicregion
2. Convenientandexpedient
3. Do not needthe namesof everyone inthe population
◦ Disadvantages
1. Representationislikelytobecome anissue
◦ Selectionprocess
2. Identifyanddefine the population
3. Determine the desiredsample size
4. Identifyanddefine alogical cluster
5. List all clustersthatmake up the populationof clusters
6. Estimate the average numberof populationmemberspercluster
7. Determine the numberof clustersneededbydividingthe samplesize bythe estimatedsize of acluster
8. Randomlyselectthe needednumbersof clusters
4 .Systematicsampling◦ SelectingeveryKthsubjectfromalistof the membersof the population
◦ Advantage
1. Veryeasilydone
◦ Disadvantages
2. subgroups
3. Some membersof the populationdon’thave anequal chance of beingincluded
◦ Selectionprocess
1. Identifyanddefine the population
2. Determine the desiredsample size
3. Obtaina listof the population
4. Determine whatKisequal toby dividingthe size of the populationbythe desiredsample size
5. Start at some randomplace in the populationlist
6. Take everyKthindividual onthe list
le,toselectasample of 25 dormrooms inyour college dorm, makesalistof all the room numbersinthe dorm.
For example there are 100 rooms,divide the total numberof rooms(100) by the numberof roomsyou wantin the

4. 4
sample (25).The answeris 4. Thismeansthat youare goingto selecteveryfourthdormroomfromthe list.Firstof all,
we have to determine the randomstartingpoint.Thisstepcanbe done bypickinganypointon the table of random
numbers,andreadacross or downuntil youcome to a numberbetween1and 4. This isyourrandom startingpoint.For
instance,yourrandomstartingpointis"3". This meansyouselectdormroom3 as yourfirstroom, andtheneveryfourth
room downthe list(3,7, 11, 15, 19, etc.) until youhave 25 rooms selected.
SamplingSize
Accordingto Uma Sekaranin ResearchMethodforBusiness4thEdition,Roscoe (1975) proposedthe rulesof thumbfor
determiningsample sizewheresample size largerthan30 and lessthan500 are appropriate formost research,andthe
minimumsize of sample shouldbe 30%of the population.
The size of the sample dependsona numberof factorsand the researchershave togive the statisticallyinformation
before theycanget an answer.Forexample,these informationlike(confidence level,standarddeviation,marginof
error andpopulationsize) todeterminethe sample size.
Types ofthe samplingin Quantitative research
Non-probabilitysamples
(Random):allowsaprocedure governedbychance toselectthe sample;controlsforsampling bias.
1. Convenience Sampling
2. Purposive sampling
3. Quota sampling
1. Convenience sampling:the processof includingwhoeverhappenstobe available atthe time …called“accidental”or
“haphazard”sampling
disadvantages…
…difficultyindetermininghowmuchof the effect(dependentvariable) resultsfromthe cause (independentvariable)
2. Purposive sampling:the processwherebythe researcherselectsasample basedonexperience orknowledgeof the
groupto be sampled…called“judgment”sampling
disadvantages…
…potential forinaccuracyinthe researcher’scriteriaandresultingsample selections
3. Quota sampling
the processwherebyaresearchergathersdatafrom individualspossessingidentifiedcharacteristicsandquotas
disadvantages…
…people whoare lessaccessible(more difficulttocontact,more reluctanttoparticipate) are under-represented
Samplingin Qualitative Research
Researchers inqualitativeresearch select their participants
accordingto their:
1) characteristics
2) knowledge
The Purposeful Samping
It iswhenthe researcherchoosespersonsorsiteswhichprovidespecificknowledge aboutthe topicof
the study.
Types ofthe Purposeful Samping
1) Maximal VariationSampling
2) Typical Sampling
3) Theoryor ConceptSampling
4) HomogeneousSampling
5) Critical Sampling
6) OpportunisticSampling
7) Snowball Sampling
1-Maximal variation Sampling
It iswhenyouselectindividualsthatdifferonacertaincharacteristic.Inthisstrategyyoushouldfirst

5. 5
identifythe characteristicandthenfindindividualsorsiteswhichdisplaythatcharacteristic.
2-Typical Sampling
It iswhenyoustudya personora site thatis “typical”to those unfamiliarwiththe situation.
You can selecta typical sample bycollectingdemographicdataor surveydata aboutall
cases.
3- Theory or ConceptSampling
It iswhenyouselectindividualsorsitesbecause theycanhelpyoutogenerate atheoryor specificconceptswithinthe
theory.Inthisstrategyyou needafull understandingof the conceptor the theoryexpectedtodiscoverduringthe study.
4- HomogeneousSampling
It iswhenyouselectcertainsitesorpeople because theypossesssimilarcharacteristics.Inthisstrategy,youneedto
identifythe characteristicsandfindindividualsorsites thatpossessit.
5- Critical Sampling
It iswhenyoustudyan exceptional case representsthe central phenomenonindramaticterms.
6- OpportunisticSampling
It isusedafterdata collectionbegins,whenyoumayfindthatyouneedtocollectnew informationtoansweryour
researchquestions.
7- Snowball Sampling
It iswhenyoudon't knowthe bestpeople tostudybecause of the unfamiliarityof the topicorthe complexityof events.
So youask participantsduringinterviewstosuggestotherindividualsto be sampled.
Ethical considerationsin data collection
 It isthe researcher’sethicalresponsibilitytosafeguardthe storytellerbymaintainingthe understoodpurpose
of the research…
 The relationshipshouldbe based ontrustbetweenthe researcherand participants.
 Informparticipantsof the purpose of the study.
 Beingrespectful of the researchsite,reciprocity,usingethical interview practices,maintainingprivacy,and
cooperatingwithparticipants.
 Patton(2002) offeredachecklistof general ethical issuestoconsider,suchas:
1. reciprocity
2. assessmentof risk
3. confidentiality,
4. informedconsent
5. data access andownership.
 Qualitative researchersmustbe aware of the potential fortheirownemotional turmoil in processingthis
information
 Duringthe interviewprocess,participantsmaydisclose sensitiveandpotentiallydistressinginformationinthe
course of the interview..