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Chapter 1 Section 3

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Title: Chapter 1 Section 3


1
Chapter 1Section 3
  • Other Effective
  • Sampling Methods

2
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

3
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.

4
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

5
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

6
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

7
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

8
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

9
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

10
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

11
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
15
Summary Chapter 1 Section 3
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