20798932 Fundamentals of Sampling Procedure

7/27/2019 20798932 Fundamentals of Sampling Procedure

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SAMPLINGSAMPLING

DR. SEEMA MUMTAZDR. SEEMA MUMTAZ


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SAMPLING PROCEDURESAMPLING PROCEDURE

HAS TO FOLLOW THREEHAS TO FOLLOW THREE

FUNDAMENTALSFUNDAMENTALS

IT IS REPRESENTATIVEIT IS REPRESENTATIVE

IS LARGE ENOUGHIS LARGE ENOUGH

THE SELECTED ELEMENTSTHE SELECTED ELEMENTSHAVE BEEN PROPERLYHAVE BEEN PROPERLYAPPROACHED, INCLUDED &APPROACHED, INCLUDED &

INTERVIEWEDINTERVIEWED


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SAMPLINGSAMPLINGSAMPLE IS A SUB SET OFSAMPLE IS A SUB SET OF

TOTAL POPULATION.TOTAL POPULATION.

IT HAS ALL INHERRANTIT HAS ALL INHERRANTQUALITIES OFQUALITIES OF

POPULATION.POPULATION.

WE CAN DERIVEWE CAN DERIVE

INFERENCES ABOUT THEINFERENCES ABOUT THE

POPULATION FROMPOPULATION FROM

SAMPLE.SAMPLE.

SAMLE HAS TO BE ASAMLE HAS TO BE A


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REQUISITE FOR A RELIABLER

EQUISITE FOR A RELIABLE

SAMPLE :SAMPLE :

EFFICIENCYEFFICIENCY REPRESENTATIVENESSREPRESENTATIVENESS

MEASURABILITYMEASURABILITY

SIZESIZE COVERAGECOVERAGE

GOAL ORIENTEDGOAL ORIENTED

FEASIBILITYFEASIBILITY ECONOMY & COSTECONOMY & COST

EFFICIENCYEFFICIENCY


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Type of samplingT

ype of sampling

procedures

procedures

Probability :Probability : each element has an equaleach element has an equalchance of being included in the sample.chance of being included in the sample.

1.1. simple random.simple random.

2.2. Systematic.Systematic.3.3. Cluster.Cluster.

4.4. Stratified.Stratified.

Non- probability :Non- probability :There is no assuranceThere is no assurancethat each element will have the samethat each element will have the samechance of being included in the sample.chance of being included in the sample.

1.1. Accidental.Accidental.

2.2. Purposive.Purposive.

3.3. Quota Sampling.Quota Sampling.


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Probability SamplingProbabilit

y Sampling

Simple Random:Sim

ple Random:

Each unit has the same chance of being selected, only decide by the lawEach unit has the same chance of being selected, only decide by the lawof chance.of chance.

Procedure:Procedure:

1.1. Prepare a sampling frame-Prepare a sampling frame-list show all the units.list show all the units.2.2. Decide on the number to be selected-Decide on the number to be selected-Sample sizeSam

ple size. It is some what. It is some whatdifficult but very critical.difficult but very critical.

Three considerations in determination of sample size:Three considerations in determination of sample size:

~ variability in the population.~ variability in the population.

~ amount of accuracy desired.~ amount of accuracy desired.

~ resource available to the researcher.~ resource available to the researcher.( table for determine sample size are available ).( table for determine sample size are available ).

~ type of study design.~ type of study design.

3.3. Selected require numbers of units, through.Selected require numbers of units, through.

~ drawing lots ( lottery method ) comes out of lotto, a game of chance.~ drawing lots ( lottery method ) comes out of lotto, a game of chance.


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Probability SamplingProbability SamplingSystematic:Systematic:A pre-determined system is followed.A pre-determined system is followed.


1.1. Have the total numbers of units in the population.Have the total numbers of units in the population.

2.2. Decide the sample size.Decide the sample size.3.3. Calculate the sampling ratio i.e. sample of 100 outCalculate the sampling ratio i.e. sample of 100 out

of 1000= 1:10of 1000= 1:10

370 out of 1600= 1:4.3 round it to the nearest whole370 out of 1600= 1:4.3 round it to the nearest wholenumbers and it will become 1:4.numbers and it will become 1:4.

4.4. Select randomly the first unit and interview everySelect randomly the first unit and interview every

fourth unit that is 1:4.fourth unit that is 1:4.


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Probability SamplingProbability Sampling

Cluster Sampling:Cluster Sampling:

Selection is made of clusters ofSelection is made of clusters ofgroups such as mohallas,groups such as mohallas,

apartment, buildings, villages,apartment, buildings, villages,housing unit etc.housing unit etc.

When a list of the entire area is notWhen a list of the entire area is notavailable and is not physicallyavailable and is not physically

possible to visit the entire area,possible to visit the entire area,one can divide the area intoone can divide the area intoseveral equal size clusters.several equal size clusters.


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Probability SamplingProbability Sampling

Stratified Sampling:Stratified Sampling:

This is done to compare different strata.This is done to compare different strata.


1.1. Population is first divided into subgroupsPopulation is first divided into subgroups(Strata) according to one or more(Strata) according to one or morecharacteristics e.g.; age, sex, economiccharacteristics e.g.; age, sex, economicstatus, religion etc.status, religion etc.

2.2. Follow a random or systematic procedureFollow a random or systematic procedureaccording to the available information.according to the available information.


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Non-ProbabilityNon-Probability

SamplingSamplingAccidental ( convenience ) Sampling:Accidental ( convenience ) Sampling:

* Sample is selected in a haphazard fashion.* Sample is selected in a haphazard fashion.

* Sample selected is unlikely to be* Sample selected is unlikely to be

representative.representative.

* The purpose of such sampling is usually less* The purpose of such sampling is usually less

cost, convenience etc.cost, convenience etc.

e.g. First ten patient in clinic,e.g. First ten patient in clinic,

Students in library.Students in library.


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NON-PROBABILITYNON-PROBABILITY

SAMPLINGSAMPLING

PURPOSIVE:PURPOSIVE: Sampling doneSampling doneon the basis of some preon the basis of some pre

determined idea (clinicaldetermined idea (clinicalknowledge etc. ).The result ofknowledge etc. ).The result of

such a sample can not besuch a sample can not be

generalized. Example:generalized. Example:

Samples from different ageSamples from different agegroups.groups.

Sample of all hypertensive.Sample of all hypertensive.


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NON-PROBABILITYNON-PROBABILITY

SAMPLINGSAMPLING

QUOTA SAMPLING :QUOTA SAMPLING : The strata ofThe strata ofthe population are identified & thethe population are identified & the

researchers determine theresearchers determine the

proportion of elements needed fromproportion of elements needed from

the various segments, eg:the various segments, eg:

If in a population of students 40%If in a population of students 40%are female & 60% are males , thenare female & 60% are males , then

the researcher may decide for athe researcher may decide for a

sample size 50 , to select 20 femalessample size 50 , to select 20 females

& 30 males .then he can use any& 30 males .then he can use any

type of probability or non-probabilitytype of probability or non-probability

sampling procedures within thesampling procedures within the

strata.strata.


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REQUISITE OF A RELIABLEREQUISITE OF A RELIABLE

SAMPLESAMPLE

EFFICIENCYEFFICIENCY

REPRESENTATIVENESSREPRESENTATIVENESS

MEASURABILITYMEASURABILITY SIZESIZE

COVERAGECOVERAGE

GOAL ORIENTEDGOAL ORIENTED FEASIBILITYFEASIBILITY

COST- EFFECTIVENESSCOST- EFFECTIVENESS

20798932 Fundamentals of Sampling Procedure

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