Paper III

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Paper III

• Qualitative research methodology

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Objective 1.5

• Discuss sampling techniques appropriate to
  qualitative research.

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• Sampling in Qualitative Research
• We will discuss three of the most common sampling
  methods used in qualitative research
• 1. Purposive sampling
• 2. Snowball sampling.

Sampling in Qualitative Research
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• As defined by Kerlinger (1986),
  purposive sampling is another non-probability
  based sampling.
• It is characterized by a deliberate effort to
  obtain representative samples through the
  inclusion of groups or typical areas in a sample.

What is purposive sampling?
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• The researcher actively selects the most
  productive sample to answer the research
  question.
• This can involve developing a framework of the
  variables that might influence an individual's
  contribution and will be based on the
  researcher's practical knowledge of the research
  area, the available literature and evidence from
  the study itself.

What is purposive sampling?
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• Purposive sample sizes are often determined on
  the basis of theoretical saturation (the point in
  data collection when new data no longer bring
  additional insights to the research questions).
• Purposive sampling is therefore most successful
  when data review and analysis are done in
  conjunction with data collection.

What is purposive sampling?
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• Purposive sampling design is usually used when a
  limited number of individuals possess the trait
  of interest.
• It is the only viable sampling technique in
  obtaining information from a very specific group
  of people.

When to use purposive sampling?
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• It is also possible to use purposive sampling if
  the researcher knows a reliable professional or
  authority that he thinks is capable of assembling
  a representative sample (this is a very
  subjective sample technique).
• The purposive sampling technique essentially is
  dependent upon the skill of the researcher to
  identify and find specific participants.

When to use purposive sampling?
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• In essence, subjects are selected because of some
  characteristic. Patton (1990) has proposed the
  following cases of purposive sampling
• Typical Case - Illustrates or highlights what is
  typical, normal, average.
• Extreme or Deviant Case - Learning from highly
  unusual manifestations of the phenomenon of
  interest, such as outstanding success/notable
  failures, top of the class/dropouts, exotic
  events, crises.
• Convenience - Saves time, money, and effort.
  Poorest rational lowest credibility. Yields
  information-poor cases.

What is purposive sampling?
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• Those who are unsuitable for the sampling study
  or who do not fit the bill have already been
  eliminated, so only the most suitable candidates
  remain.
• As the most appropriate people for the study have
  been selected, this process becomes a lot less
  time consuming.

Advantages of purposive sampling
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• The results of purposeful sampling are usually
  expected to be more representative of the
  population than those achieved with an
  alternative form of sampling.
• If you are looking for a very rare or much sought
  after group of people for a particular research
  study, using purposive sampling may usually be
  the only way you can track them down.

Advantages of purposive sampling
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• Quite often market researchers use this type of
  sampling in order to target a particular group of
  people.
• Basing their results on what this group has said,
  their findings will then be used as a
  representation of the rest of the population.
• Deciding in advance what group to target based on
  the types of results a company is expecting to
  find will help them save costs and get the job
  done as soon as possible.

Advantages of purposive sampling
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• Quite often market researchers use this type of
  sampling in order to target a particular group of
  people.
• Basing their results on what this group has said,
  their findings will then be used as a
  representation of the rest of the population.
• Deciding in advance what group to target based on
  the types of results a company is expecting to
  find will help them save costs and get the job
  done as soon as possible.

Limitations of purposive sampling
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• The selection criteria the researcher uses can be
  very arbitrary and are almost always subjective.
• The narrowness of the questions used will reflect
  the researcher's particular stance on a subject
  far more than a random sample.

Limitations of purposive sampling
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• The sample population used may not necessarily be
  entirely the population that the researcher is
  trying to reach.
• As such, since such a small sample population is
  often used, a small variation in the sample will
  cause deviance in the results.

Limitations of purposive sampling
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• Snowball sampling is a non-probability sampling
  technique that is used by researchers to identify
  potential subjects in studies where subjects are
  hard to locate.
• This type of sampling technique works like chain
  referral. After observing the initial subject,
  the researcher asks for assistance from the
  subject to help identify people with a similar
  trait of interest.

Snowball sampling
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• The process of snowball sampling is much like
  asking your subjects to nominate another person
  with the same trait as your next subject.
• The researcher then observes the nominated
  subjects and continues in the same way until the
  obtaining sufficient number of subjects.
• The snowball sampling technique essentially is
  dependent upon the participants to identify and
  find specific participants.

Snowball sampling
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• The process of snowball sampling is much like
  asking your subjects to nominate another person
  with the same trait as your next subject.
• The researcher then observes the nominated
  subjects and continues in the same way until the
  obtaining sufficient number of subjects.
• The snowball sampling technique essentially is
  dependent upon the participants to identify and
  find specific participants.

Snowball sampling
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Snowball sampling

• When can this type of sampling be useful?

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• If obtaining subjects for a study that wants to
  observe a rare disease, the researcher may opt to
  use snowball sampling since it will be difficult
  to obtain subjects.
• It is also possible that the patients with the
  same disease have a support group being able to
  observe one of the members as your initial
  subject will then lead you to more subjects for
  the study.
• Snowball sampling is often used with focus groups
  in qualitative research methods.

Application of Snowball sampling
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• Advantages of snowball technique
• The chain referral process allows the researcher
  to reach populations that are difficult to sample
  when using other sampling methods.
• The process is cheap, simple and cost-efficient.
• This sampling technique needs little planning
  compared to other sampling techniques.

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• Limitations of snowball technique
• Representativeness of the sample is not
  guaranteed. The researcher has no idea of the
  true distribution of the population and of the
  sample.
• Sampling bias is also a fear of researchers when
  using this sampling technique.
• Initial subjects tend to nominate people that
  they know well. Because of this, it is highly
  possible that the subjects share the same traits
  and characteristics, thus, it is possible that
  the sample that the researcher will obtain is
  only a small subgroup of the entire population.