Chapter 1 Section 3

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Chapter 1Section 3

• Other Effective
• Sampling Methods

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Chapter 1 Section 3

• A stratified sample is obtained when we choose a
  simple random sample from subgroups of a
  population

• A stratified sample is obtained when we choose a
  simple random sample from subgroups of a
  population
• This is appropriate when the population is made
  up of nonoverlapping (distinct) groups called
  strata

• A stratified sample is obtained when we choose a
  simple random sample from subgroups of a
  population
• This is appropriate when the population is made
  up of nonoverlapping (distinct) groups called
  strata

• A stratified sample is obtained when we choose a
  simple random sample from subgroups of a
  population
• This is appropriate when the population is made
  up of nonoverlapping (distinct) groups called
  strata

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Chapter 1 Section 3

• Example polling a population about a political
  issue
• It is reasonable to divide up the population into
  Democrats, Republicans, and Independents. Then
  we take a SRS from within each stratum.

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Chapter 1 Section 3

• Assume that the sizes of the strata are
• Resident students 5,000
• Commuter students 4,000
• Faculty and staff 1,000
• If we wish to obtain a sample of size n 100
  that reflects the same relative proportions, we
  would want to choose
• 50 resident students
• 40 commuter students
• 10 faculty and staff

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Chapter 1 Section 3

• A systematic sample (or 1-in-k design) is
  obtained when we choose every kth individual in a
  population
• The first individual selected corresponds to a
  random number between 1 and k

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Chapter 1 Section 3

• Example polling customers about satisfaction
  with service
• We do not have a list of customers arriving that
  day
• We do not even know how many customers will
  arrive that day
• Simple random sampling (and stratified sampling)
  cannot be implemented

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Chapter 1 Section 3

• A cluster sample is obtained when we choose a
  random set of groups and then select all
  individuals within those groups
• We can obtain a sample of size 50 by choosing 10
  groups of 5
• Cluster sampling is appropriate when it is very
  time consuming or expensive to choose the
  individuals one at a time

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Chapter 1 Section 3

• A convenience sample is obtained when we choose
  individuals in an easy, or convenient way

• A convenience sample is obtained when we choose
  individuals in an easy, or convenient way
• Self-selecting samples are examples of
  convenience sampling
• Individuals who respond to television or radio
  announcements

• A convenience sample is obtained when we choose
  individuals in an easy, or convenient way
• Self-selecting samples are examples of
  convenience sampling
• Individuals who respond to television or radio
  announcements
• Just asking around is an example of convenience
  sampling
• Individuals who are known to the pollster

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Chapter 1 Section 3

• Convenience sampling has little statistical
  validity
• The design is poor
• The results are suspect
• However, there are times when convenience
  sampling could be useful as a rough guess
• If none of your co-workers are concerned about a
  particular issue, then it is possible that the
  set of all employees would not be concerned about
  that issue

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Chapter 1 Section 3

• A multistage sample is obtained using a
  combination of
• Simple random sampling
• Stratified sampling
• Systematic sampling
• Cluster sampling
• Many large scale samples (the US census in
  noncensus years) use multistage sampling

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Summary Chapter 1 Section 3

• There are other sampling methods that are
  particularly useful in certain situations
• Stratified sampling to cover the different strata
• Systematic sampling when the frame is unknown
• Cluster sampling to reduce the time and expense
  required
• Multistage sampling for effective large scale
  samples
• The choice of sampling methods depends on the
  structure of the population and the goals of the
  analyst

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Summary Chapter 1 Section 3
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Summary Chapter 1 Section 3
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Summary Chapter 1 Section 3
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Summary Chapter 1 Section 3