Probability Sampling Sheldon

7/24/2019 Probability Sampling Sheldon

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PROBABILITY

SAMPLING

Sheldon Manickam


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SAMPLING


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WHY SAMPLING?

It would be impracticable for you to survey the entirepopulation

Your budget constraints prevent you from surveyingthe entire population

Your time constraints prevent you from surveying the

entire population

You have collected all the data but need the resultsquickly


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DEFINITIONS YOU SHOULD KNOW

Element:The obect aboutwhich or from which theinformation is desired! e"g"! therespondent

Sampling unit:#n element! ora unit containing the element!that is available for selection at

some stage of the samplingprocess

Sampling Frame: $istcontaining all the elements from

which you choose the sample


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PROBABILITY SAMPLING

%&robability sampling 'or representativesampling( is most commonly associated withsurvey)based research strategies where you needto make inferences from your sample about apopulation to answer your research question's(

or to meet your obectives"*


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FOUR STAGES OF PROB. SAMPLING

+ ( Identify a suitable sampling frame based on yourresearch question's( or obectives"

, ( -ecide on a suitable sample si.e"

/ ( Select the most appropriate sampling techniqueand select the sample"

0( 1heck that the sample is representative of the

population"


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SUITABLE SAMPLE SIZE

The larger your sample2s si.e! the lower the likelyerror in generali.ing to the population

&robability sampling is therefore a compromisebetween the accuracy of your findings and the

amount of time and money you invest incollecting! checking and analy.ing the data"


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&robabilitySampling

Simple3andom

SystematicStratified3andom

1luster Multi)stage

TYPES OF PROB. SAMPLING


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PROBABILITY SAMPLING

4ach element in the population has a known andequal probability of selection"

4very element is selected independently of everyother element"


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SYSTEMATIC SAMPLING

+( 5umber each of the cases in your sampling frame with aunique number" The first case is numbered 6! the second +and so on"

,( Select the first case using a random number"

/( 1alculate the sampling fraction"

sampling fraction 7actual sample si.e total population

0( Select subsequent cases systematically using the

sampling fraction to determine the frequency of selection"


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STRATIFIED RANDOM SAMPLING

+( 1hoose the stratification variable or variables"

,( -ivide the sampling frame into the discrete strata"

/( 5umber each of the cases within each stratum

with a unique number"

0( Select your sample using either simple random orsystematic sampling"


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CLUSTER SAMLPING

+( 1hoose the cluster grouping for your samplingframe"

,( 5umber each of the clusters with a uniquenumber" The first cluster is numbered 6!

the second + and so on"

/( Select your sample using some form of randomsampling"


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MULTI-STAGE SAMPLING

#lso called multi)stage cluster sampling

8sed to overcome problems associated with ageographically dispersed population when face)to)face contact is needed or where it is e9pensive

and time consuming to construct a samplingframe for a large geographical area


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MULTI-STAGE SAMPLING

49ample: &opulation is very large! sample si.e isvery small

To select ;6 people from all over India

Select , people from each state randomly


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Probability Sampling Sheldon

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