Sampling Bias

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Sampling Bias
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• Sampling is the process of selecting a number of
  individuals for a study in such a way that the
  individuals represent the larger group from which
  they were selected.
• The purpose of sampling is to gain information
  about a larger population.

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Avoiding Sampling Error and Bias

• Sampling error is beyond the control of the
  researcher.
• It is a reality of random sampling.
• If the population is well selected and
  sufficiently large, chances are the sample will
  closely represent the population.

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Sampling Bias

• Does not result from random differences between
  samples and populations.
• It is not random and usually the fault of the
  researcher.

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Examples of Sampling Bias

• Study is designed to determines all college
  students attitudes on drinking.
• Researcher polls students outside a bar. All
  college students are not represented in this
  sample.

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Example of bias

• A researcher gets only 45 percent of the surveys
  she sent out returned. The large number of
  non-returns represents sampling bias.

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• If it is not possible to avoid sampling bias, the
  researcher must decide whether the bias is so
  severe that the results of the study will be
  seriously affected.
• If the decision is to continue, the bias should
  be reported in the final research report.

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Strategies for Reducing Bias in Qualitative
Research Studies.
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• Extend the study. Stay in the field for a longer
  time period. Obtain additional data that can be
  compared to earlier data or to compare
  participants consistency of responses.

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• Include additional participants to broaden the
  representativeness of the study and the database.

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• Make a concerted effort to obtain participant
  trust, thus providing more detailed honest
  information from participants.

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• Work with another researcher and independently
  gather and compare data collected from subgroups
  and participants.

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• Allow participants to review and critique field
  notes or tape recordings for accuracy and
  meaning, but only at the end of the entire data
  collection period.

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• Use verbatim accounts of observations or
  interviews by collecting and recording data with
  tape recordings and detailed field notes,
  including quotes.

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• Record in a journal ones own reflections,
  concerns, and uncertainties during the study and
  refer to them when examining the data collected.

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• Examine unusual or contradictory results for
  explanations.

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• Use different data sources to confirm one another.

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Descriptive Research

• Reducing Observation Bias

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• Observation bias refers to invalid observations
  that result from the observers perceptions,
  beliefs, and biases, rather than from what is
  objectively observed.

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• Observers effect occurs when the presence of the
  observer makes the persons being observed behave
  atypically because they are being observed. The
  best way to handle the problem is to make
  observers aware of it so that they can attempt to
  be as unobtrusive as possible.