Experimental epidemiological studies involve investigators designing research with control over protective factors being studied. Subjects are randomly assigned to exposed and unexposed groups to eliminate confounding. Types of experimental studies include randomized controlled trials (RCTs) that evaluate therapies, controlled field trials (CFTs) of preventive interventions like vaccines, and community trials (CTs) involving whole communities, one exposed to a factor and one unexposed. These studies provide strong evidence when confounding is not an issue as in observational studies.

1. Experimental epidemiological
methods
Professor Maja Miskulin, MD, PhD

2. History
James Lind – 1747.
one of the first noted,
controlled clinical experiment
in the history of medicine

3. Experimental studies
confounding factors are usually not a problem in
experimental studies
epidemiologists usually study human populations (mainly
through observational studies)
experimental studies are largely used in basic medical
sciences where investigators design researches on animal
models

4. Experimental studies
in experimental studies, the investigator has "control" over
the protective factor that is being investigated
the investigator determines which of the subjects will get a
drug that is being investigated, and who does not
the control group gets either placebo or the best existing
drug on the market – so called gold standard

5. Experimental studies
the best way to classify subjects in the investigated groups
(exposed to investigated drug and unexposed) is
randomization, which indicates the random distribution of
the subjects in the groups
randomization is primarily used to eliminate the effects of
confounding factors

6. Experimental studies
when we use experimental studies in epidemiology, we can
get very strong evidence
these studies should not be implemented until the
probability of a causal or risk relationship has been well
determined using the other types of study designs

7. Types of experimental studies
randomized controlled trial (RCT)
controlled field trial (CFT)
community trial (CT)

8. 
Randomized controlled trial (RCT)
the main goal of RCT is to evaluate the therapeutic
approach to the patients who are included in the study
individually
in RCT, we can investigate the effect of drugs, surgical
procedures, certain physical therapeutic methods and other
therapeutic approaches

9. 
Controlled field trial (CFT)
in CFT we want to estimate the effect of preventive
intervention most commonly on healthy subjects, which are
included in the study individually
CFT was most frequently applied when investigating the
efficacy of a vaccine

10. 
Controlled field trial (CFT)
The Salk Polio Vaccine Field
Trial - Jonas Salk administers
his polio vaccine on February
26, 1957 in the Commons
Room of the Cathedral of
Learning at the University of
Pittsburgh where the vaccine
was created by Salk and his
team

11. 
Controlled field trial (CFT)
unlike RCT, CFT most commonly includes healthy subjects,
and sampling is carried out from the population
when investigating the efficacy and safety of the vaccine, we
need to divide the healthy subjects into two groups, one that
will get the active substance (exposed group) and the other
who will be given placebo (unexposed group)

12. Controlled field trial (CFT)
in this type of experimental study we can show results in
several ways:
relative risk
survival curves
effectiveness of the investigated vaccine (calculation of
the population preventable fraction - PPF)

13. Population preventable fraction (PPF)
tells us about the proportion of newly diagnosed cases of
the disease that can be prevented at the population level if
we apply a preventative measure in that population
𝑃𝑃𝐹 % =
𝑝 1 − 𝑅𝑅
𝑝 1 − 𝑅𝑅 + 𝑅𝑅
× 100
p – the proportion of the population that is exposed to the protective factor
RR – relative risk

14. Community trial (CT)
the community trial is a type of experimental study that
involves at least two whole communities, one exposed and
the other unexposed
some of the protective factors cannot be investigated on
individuals because all inhabitants of a particular geographic
area are exposed to such factors

15. Community trial (CT)
in this case, all inhabitants of a geographic area that is
exposed to a protective factor are included in the study, and
as a control group all inhabitants of another geographic area,
where such a factor is lacking

16. Community trial (CT)
one of the best known
community trials began in
1944 in the United States,
and that was a study of the
effect of water fluorination
on health of the teeth in
children

17. Natural experiment
the natural experiment is not a type of experiment studies
the term natural experiment refers to the implementation
of observational epidemiological studies in case of
unfortunate events, such as natural disasters (e.g. flood, fire
or earthquake), or accidents caused by human error and
neglect (for example, Chernobyl catastrophe and methyl-
mercury poisoning in the Gulf Minamata in Japan)

18. Experimental studies ? (mark the correct answer)
 confounding factors are usually big problem in experimental
studies
WRONG
confounding factors are usually not a problem in experimental
studies
CORRECT

19. Controlled field trial (CFT)? (mark the correct answer)
CFT was most frequently applied when investigating the
efficacy of a vaccine
CORRECT
CFT was most frequently applied when investigating the
efficacy of a surgical procedure
WRONG

20. Community trial (CT)? (mark the correct answer)
the community trial is a type of analytical study that involves at
least two whole communities, one exposed and the other
unexposed
WRONG
the community trial is a type of experimental study that
involves at least two whole communities, one exposed and the
other unexposed
CORRECT

21. Thank You for Your kind attention!