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Chapter 9

IHS 4504 Chapter Notes - Chapter 9: Blind Experiment, Clinical Trial, Internal Validity

Interdis. Health Sciences
Course Code
IHS 4504
Jayanta Gupta

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Placebo Effect
- Placebo effect: differences caused by participants’ expectations instead of any provided
o Placebo: something that looks like the actual treatment, but in reality, has no
effect; often used in drug studies.
- Blind study: those involved in the study do not know whether they are receiving the
treatment or the placebo.
- Double blind study: neither the researcher nor the participants know who is receiving
the real treatment and who is receiving a placebo.
Diffusion of Treatment
- Diffusion treatment: occurs when the treatment being applied to one group spills over
to or contaminates another group.
- Controlling for a diffusion effect can be difficult, particularly if those in the experimental
and control groups live or work together.
- Location effect: occurs when there are differences in the locations where interventions
take place.
- Implementation effect: a threat to internal validity that occurs when those responsible
for implementing the experimental treatment inadvertently introduce inequality or bias
into the study.
- This can happen in two ways:
o First, if there are multiple people providing the treatment program or
intervention, they may not be equal in their knowledge levels, understanding of
the program, personality traits, presentation skills, and so forth.
o The second way implementation bias can occur is if an individual implementing
the intervention inadvertently favors one group over another.
- To control for this implementation threat, whenever possible, have someone other than
the program developer presents the program.
Threats to External Validity
- The first of the three threats to external validity is selection treatment interaction.
o Selection treatment interaction: external threat to validity that concerns the
ability of a researcher to generalize the results of a study beyond the groups
involved in the study due to the way the study groups were selected.
- If, one the other hand, a study uses a random sample of participants, results can
legitimately be generalized to the group from which the random sample was selected.
o 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 generalized.
Setting Treatment Interaction
- A second threat to external validity described by Creswell is the setting treatment
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