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This lecture seeks to provide you with a basic understanding of
Experimental Studies, the most respected type of research study used by
Epidemiologists. Additional textbook resources can be found in thefollowing annotated bibliographies on my Web site:Annotated Biostatistics Bibliography
Annotated Epidemiology Bibliography
Annotated Research Methods
Annotated Research Practice (A - L
http://www.bettycjung.net/Biostats.htmhttp://www.bettycjung.net/Epi.htmhttp://www.bettycjung.net/Methods.htmhttp://www.bettycjung.net/Research.htmhttp://www.bettycjung.net/Research.htmhttp://www.bettycjung.net/Research.htmhttp://www.bettycjung.net/Research.htmhttp://www.bettycjung.net/Research.htmhttp://www.bettycjung.net/Methods.htmhttp://www.bettycjung.net/Epi.htmhttp://www.bettycjung.net/Biostats.htm8/13/2019 Experimental Study - TEO
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Just like other scientific disciplines, Public Health support the work of
researchers in its field. Just like other academic disciplines, Public Health
includes many specialty areas, each conducting their own research, i.e.,
health education, health policy, etc. But, if you had to choose one area
that is most close to the heart of what Public Health is all about, its
Epidemiology.
While Epidemiology is the study of the distribution of disease, the
research methods used and developed by epidemiologists have been used
also to study disease-related issues. For example, health servicesresearchers look at how health services differ for different populations.
Health education researchers look at how people react to disease and
how these behaviors impact quality of life.
Thus, findings from epidemiological studies should serve as the
foundation for research in health education, health policy, etc. because a
better understanding of how disease impacts populations is crucial before
we can even think of how to better deliver services, educate people about
health behaviors, and develop rational public policy.
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It can be said, in general, that there are two main types of
studies.
Observational studies are those in which the researchers do not
interfere or manipulate any of the factors under study. They
record their observations of whats going on, and explain what
they observe with measures of association.
While we would like to say that A causes B, in order for thesekinds of studies to attempt such an explanation, there would
have to be many, many studies that observed the same chain of
events before there is a consensus that A causes B, if that.
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Interventional studies are when researchers attempt to show that A
causes B by actually manipulating those factors they think have
something to do with causing some outcome. These usually look athow well some treatment work.
In Public Health, its difficult to show that a specific factor caused a
particular outcome, when we are talking about populations. There are
usually many factors that can result in a particular outcome. And
because it is unethical to conduct testing on human subjects without
peoples consent, conducting research involving general populations is
infeasible as well. So, from a feasibility standpoint, observational
studies are more common, and if done well, can provide us with
insights on how to control disease and improve quality of life.
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Experiments, or randomized trials are used for many purposes.
Such purposes include: Assessing new screening and early
detection programs, evaluating new drugs and other treatmentsof disease, or new ways of organizing and developing health
services.
The randomized trial is considered the gold standard for
evaluating the effectiveness of therapeutic, preventive and othermeasures, both in Clinical Medicine and in Public Health.
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Observational studies include cross-sectional, case-control and cohort
studies. Of these 3 study designs, the cohort method is the preferred
design for confirming causal (antecedent) associations of healthoutcomes.
An extension of the cohort design would be an experiment to see
whether the expected outcome is found in a group receiving the
exposure (antecedent) with a control group not receiving the exposure.
A natural experiment would follow a cohort exposed to a natural
phenomenon of health consequences and then compare the health
effects in the exposed population with those not exposed to the
phenomenon.
Experimental studies are referred to as experimentalepidemiology. They are applied as clinical trials to assess the
efficacy of some intervention (or procedure), as surgical technique,
type of facility, or type of health service, to name a few. The more
common term used in Epidemiology is randomized trial.
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This is the basic strategy behind an experimental epidemiological
study. To show that a treatment is effective, the improvement rate in a
treated group (T) should be greater than the improvement rate in theuntreated group (NT), and that the differences in rates should be
unlikely they are due to chance.
The control group (NT) should be similar to the treatment group (T) in
all characteristics associated with the expected outcome (recovery),
and should not receive the studied treatment. The control group maybe receiving the prevailing, or current standard of care, or a placebo.
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To cover the basics, I am trying to keep this as simple as possible.
Randomized trials, especially clinical trials, can become very complex,
with many groups (arms) involved in one study. Regardless of how manygroups are in a study, random allocation (or randomization) is used to
ensure the groups are comparable.
In matching, the researcher may match for, say, race and sex. So for a
matched pair of white females, the researcher would then randomly
assign one subject to the treatment group and the other to the controlgroup. After all the matched pairs have been assigned, the two study
groups would then have the same race and age distribution, as well as
about the same distribution for other variables because of random
allocation.
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This graphic shows when random allocation (randomization) should take
place during the study process. Basically, the researcher starts with adefined population that is randomized to a new treatment or current
treatment. The subjects are then followed to see how many improve for
the new treatment and current treatment. Sometimes a treatment may be
compared to no treatment, but this is very rare. If there is already a
treatment in place, it is best to compare the new treatment to a treatment
already in place.
Randomization increases the likelihood that the groups will be
comparable in regard to characteristics that may affect prognosis. Such
characteristics include sex, age, race and severity of disease.Then again randomization isnt a guarantee of comparability because
chance does play a role in the process. In the long run, the groups tend to
be similar. Finally, randomization is ethical only when we do not know
whether one treatment is better than the other.
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Despite the negatives, randomized controlled studies are still considered
the gold standard of clinical research. If done right, results, whether good
or bad, contributes to the collective scientific body of knowledge.
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