IHS 4504 Chapter Notes - Chapter 7: Nonprobability Sampling, Clinical Trial, Sampling Bias
DepartmentInterdis. Health Sciences
Course CodeIHS 4504
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Chapter 7- Selecting Study participants
Identifying the participants
- However, since most clinics have patients with a variety of different demographic, and
other defining variables, you will need to further, types of health insurance, you will
need to further identify those individuals to be included in your study.
o Inclusion criteria: those that include participants.
o Exclusion criteria: those that exclude participants
Census Versus Sample
- Once the decision has been made on the inclusion/exclusion criteria, then a decision
must be made as to how the specific participants for the study will be selected.
- Census: all the potential participants
- Sample: some of the potential participants
- Sampling unit: the element or set of elements considered for selection as part of a
- Image below illustrates the relationship among groups of individuals who have the
potential to be in your study.
- Universe: all the participants with the given inclusion criteria that are unspecified by
place or time.
- Study population: those in the population who are accessible to the researcher who had
the potential of being selected for the study, and to whom the results can be
- Population: those individuals in the universe that are specified by time and place.
- Sampling: the process by which the sample is selected
- Sampling error: the difference between the sampling estimate and the actual study
- Sampling bias: a sampling process that ends with a group that is biased.
- These sampling methods are categorized into two major groups- probability and
o Probability sampling: uses random selection of participants and ensures that
each person in the study population has an equal chance and known probability
of being selected.
o Nonprobability sampling: all individuals in the study population do not have an
equal chance and a known probability of being selected to participate in the
- The common element of all probability sampling is the random sampling of participants.
o Random selection: when every member of the population has an equal chance
to be selected as part of the sample.
- Random assignment: the assignment of the participants as an equal chance of being
assigned to any of the groups.
- Randomization: the process of randomly assigning research participants of the sample.
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