Sampling and types of techniques

A sample is a subset of individuals from a larger population. Sampling means selecting the group that you will actually collect data from in your research.

1. PRESENTED BY
MR.KALYAN KUMAR MSC(N)
Sampling techniques

2. Samplingisprocessofselectingrepresentative
unitsfromentirepopulationofastudy.Inresearch
studies,itisnotalwayspossibletostudyanentire
populationthereforetheresearcherdrawsa
representativepartofpopulationthroughsampling
process.

3. Types of sampling techniques
Probability sampling
I.Simple random
sampling
II.Stratified random
sampling
III.Systematic random
sampling
IV.Cluster sampling
V.Sequential sampling
Non probability
sampling
I.Purposive sampling
II.Convenient sampling
III.Consecutive sampling
IV.Quota sampling
V.Snow ball sampling

4. Probabilitysampling:
Itinvolvesrandomselectionofelements.Every
subjectinpopulationhasequalchancetobeselected
asstudysample.

5. I. Simple random sampling
Everypopulationmemberhasaequalchanceof
beingselectedasasubject.
Prerequisitesanduses:
Populationshouldbehomogenous
Musthavelistofelements/membersofaccessible
population
Randomselectioneitherbylottery,randomtable
orcomputer

6. Advantages
Mostreliableandunbiasedmethod
Requiresminimumknowledgeofstudypopulation
Freefromsamplingerrors/bias.
Disadvantages
Expensiveandtimeconsuming.

7. II. Stratified random sampling
Dividingheterogeneouspopulationinstratabased
onselectedtraitssuchasage,gender,habitatand
thenRandomselectionofsamplefromeachStrata.
Prerequisitesanduses:
Usedforheterogeneouspopulation
Advantages:
Ensuresrepresentativesampleinheterogeneous
population
Comparisonispossibleintwogroups.

8. Disadvantages:
Requires complete information of population
Large population is required
Chances of faulty classification of strata.

9. III.Systematic random sampling
SelectingofeveryKthcasefromthegroup,suchas
every10
th
persononapatientlistorevery100
th
person.
Prerequisitesanduses
Listoftargetpopulationmustbeavailable
Random distributionsubjectsratherthan
segregation.

10. Advantages
Convenientandsimpletocarryout
Distributionofsampleoverentirepopulation.
Disadvantages
Lessrepresentativesampleifsubjectsarenonrandomly
distributed.

11. IV.Cluster sampling
Whensimplerandomsamplingisnotpossibledueto
thesizeofthepopulation,clusterrandomsampling
iscarriedout.Clustersamplingmeansrandom
selectionofsamplingunitconsistingofpopulation
elements.
Prerequisitesanduses
Whenpopulationisaverylarge
Randomselectionofsubjectsfromselectedclusters
Advantages
Cheap,quickandeasyforalargepopulation.

12. Disadvantages
Possibilityofhighsamplingerror
Ifasmallhomogenouspopulationisunderstudy,
thistechniqueisnotatalluseful.

13. V. Sequential sampling
Thismethodofsampleselectionisslightlydifferentfrom
othermethods.Herethesamplesizeisnotfixed.The
investigatorinitiallyselectssmallsampleandtriesoutto
makeinferences;ifnotabletodrawresults,heorshe
thenaddsmoresubjectsuntilclear-cutinferencescanbe
drawn.

14. Advantages
Facilitatethereferencesforstudyonbestpossible
smallestsample.
Disadvantages
Notpossibletostudyaphenomenon,whichneedstobe
studiedonepointoftime.
Requirestherepeatedentryintothefieldtocollectthe
sample.

15. Nonprobabilitysamplingtechniquewherein
thesamplesaregatheredinaprocessthatdoesnot
giveallindividualsinthepopulationwithequal
chancesofbeingselectedinthesample.Elements
arechosenbychoicenotbyachance.

16. I. Purposive sampling
Subjectsarechosentobepartofthesamplewith
specificpurposeinmind.Itisalsoknownas
‘Judgmental’or‘Authoritative’sampling.Samplesare
chosenbychoicenotbychance.
Prerequisitesanduses
Requiresin-depthknowledgeabouttheaccessible
population
Usedwhenalimitednumberofindividualsapossess
thetraitofinterest.

17. Advantages
Simpletodrawasample
Savesresourcesasitrequireslessfieldwork.
Disadvantages
Requiresconsiderableknowledgeaboutthepopulation
understudy
Itisnotalwaysreliablesample.

18. II.Convenience sampling
Subjectsareselectedbecauseoftheirconvenient
accessibilityandproximitytotheresearcher.
Thesubjectsarechoosejustbecauseofthefactthat
thereareveryeasytorecruitforthestudy.Sometimes,it
isalsoknownasan‘accidentalsampling’.

19. Advantages
Easiest,cheapestandleasttimeconsuming
Helpsinsavingtime,moneyandresources.
Disadvantages
ChancesofSamplingbias
Findingscan’tbegeneralized.

20. III.Consecutive sampling
Itisverysimilartoconveniencesampling,except
thatitseekstoincludeallaccessiblesubjectsasa
partofthesample.Thisnonprobabilitysampling
techniquecanbeconsideredasthebestofallnon
probabilitysamplesbecauseitincludesallthe
subjectsthatareavailable.Itisalsoknownas‘total
enumerative’sampling.

21. Advantages
Ensuresmostrepresentativesample
Convenientandlesstimeconsuming.
Disadvantages
Theresearcherhasnosetplansaboutsamplesize
andsamplingschedule.

22. IV.Quota sampling
Equalorproportionaterepresentationofsubjects
fromeachquota.Thebasesofthequotaareusually
age,gender,education,race,religionandsocial
economicstatus.

23. Advantages
Economicallycheapeconomic
Suitableforstudieswherefieldworkhastobe
carriedout.
Disadvantages
Alwaysdoesnotguaranteerepresentativesample
ChancesofSamplingbias.

24. V.Snowball sampling
Itisusedbyresearcherstoidentifypotentialsubjects
instudieswheresubjectsarehardtolocate.suchas
commercialsexworkers,drugabusersetc.
ThistypeofSamplingtechniqueworklikechain
referral.Thereforeitisalsoknownas‘chain
referral’sampling.Theresearcherasksfor
assistancefromthesubjecttoidentifypeoplewith
similartraitofinterestafterobservingtheinitial
subject.
Askingsubjectstonominateanotherpersonwiththe
sametrait.

25. Typesofsnowballsampling
1.Linearsnowballsampling
2.Exponentialnondiscriminativesnowballsampling
3.Exponentialdiscriminativesnowballsampling.

26. Advantages
Theprocessissimple,cheapandcosteffective
Thesamplingtechniquerequiresalesserworkforce.
Disadvantages
Littlecontrolofresearcheroverthesampling
method
Representativenessofthesampleisnotguaranteed
Chancesofpoorcoverageofentirepopulation.

27. Summary
Conclusion