Business and Economic Statistics:

Stratified and Clustered Sampling

Presenter: Sam Capurso

Objectives

• Be able to explain and apply the• following concepts:

- Stratified Sampling- Clustered Sampling

• Give examples of strata and clusters• Explain why you would use Stratified Sampling

and Clustered Sampling

Use this as...

• A refresher

• Or

• To resolve any knowledge gaps you have

Stratified Sampling

• Split the population into groups (strata) whereby:- Each stratum is the same

within- Each stratum is different

between

• Take a SRS from each stratum

• Be careful! You can’t have more than one of the same strata

StrataDifferent characteristics

Clustered Sampling• Select or construct groups

(clusters) whereby:- Each cluster is roughly the

same as the others- The clusters are

representative of the entire population

• Randomly select clusters and then take a census of these

• Be careful! CS is not SRS!

Clusters

RandomSelection

Application

• What are some examples of strata?

• What are some examples of clusters?

• Scenario: You want to survey nurses in Australian hospitals to ask their attitudes towards their work conditions and pay

Why conducted Stratified Sampling?

• You have reason to believe that people of a similar characteristic will respond in a particular way

• You want to reduce variability in the samples

• You want to reflect proportions of groups in the population

?

Why conducted Clustered Sampling?

• Reduce costs

• Convenience (not convenience sampling!)

• Practicality

$

SummaryStratified Sampling (SS) Clustered Sampling (CS)

Groups same within: homogenous

Groups have no defining characteristic – are representative of population: heterogeneous

Groups are different from each other

Groups are roughly the same as each other

SRS taken from each group Census taken from each group

Know examples of strata Know examples of clusters

Know reasons for conducting Stratified Sampling

Know reasons for conducting Clustered Sampling

End

Please note_(this was shown before the presentation)

• As you know, I am currently undertaking a Certificate IV in Training and Assessment at TAFE SA

• This presentation is being recorded, and will be submitted for assessment

Terminology_slide 4 (for assessor only)

Population

Simple Random

Sample (SRS)

Stratified

Sampling

Stratum & strata

Clustered

Sampling

Census

New terms in bold