Experimental epidemology

EXPERIMENTAL
EPIDEMIOLOGY
DR SAKSHI KAUR CHHABRA
2ND YR PG STUDENT
DEPARTMENT OF PUBLIC HEALTH DENTISTRY
PACIFIC DENTAL COLLEGE AND HOSPITAL,DEBARI
2

[1] INTRODUCTION
[2] AIMS
[3] EXPERIMENTAL STUDIES – TYPES
[4] RANDOMIZED CONTROLLED TRIALS
[5] NON- RANDOMIZED TRIALS
[6] USES OF EXPERIMENTAL
EPIDEMIOLOGY
[7] ADVANTAGES AND DISADVANTAGES
[8] CONCLUSION
[9] REFERENCES

• In the 1920s, "experimental epidemiology" meant the study of epidemics
among colonies of experimental animals such as rats and mice. In
modern usage, experimental epidemiology is often equated with
RANDOMIZED CONTROLLED TRIALS .
• Experimental or intervention studies are similar in approach to cohort
studies excepting that the conditions in which study is carried out are
under the direct control of the investigator.

 An experiment is the best epidemiological study design to prove causation.
 It can be viewed as the final or definitive step in the research process.
 A mechanism for confirming or rejecting the validity of ideas, assumptions,
postulates and hypotheses about the behaviour of objects, or effects upon them
which result from interventions under defined sets of conditions.

[A] TO PROVIDE SCIENTIFIC PROOF
[B] TO PROVIDE A MEASURING
METHOD

Experimental studies are of two types :
[1] Randomized controlled trials
[2]Non-randomized or "non-experimental" trials

One of the essential features of a randomized controlled trial
is that the study is conducted under a strict protocol.
The protocol specifies:-
[a] the aims and objectives of the study
[b] questions to be answered
[c] criteria for the selection of study and control groups
[d] size of the sample
[e] the procedures for allocation of subjects into study and
control groups
[f] treatments to be applied

The protocol also specifies:-
[g] standardization of working procedures
[h] schedules as well as responsibilities of the parties involved
The protocol aims at
 preventing bias
 to reduce the sources of error in the study.

Population to which the findings of the trial, if found successful, are expected to be
applicable. EXAMPLE
• geographically limited
• population of a whole city
• a population of school children
• industrial workers
[A] REFERENCE OR TARGET
POPULATION

• It is derived from the reference population.
• It is the actual population that participates in the experimental study.
• Ideally, it should be randomly chosen from the reference population, so that it
has the same characteristics as the reference population.
• If the study population differs from the reference population, it may not be
possible to generalise the findings of the study to the reference population.
[B] EXPERIMENTAL OR STUDY
POPULATION

 Randomization is a statistical procedure by which
the participants are allocated into groups usually
called "study" and "control" groups, to receive
or not to receive an experimental preventive or
therapeutic procedure, manoeuvre or
intervention.
 Randomization is an attempt to eliminate "bias"
and allow for comparability.

 Randomization is the "heart" of a control trial.
 It will give the greatest confidence that the
groups are comparable so that "like can be
compared with like".
 In other words, by random allocation, every
individual gets an equal chance of being allocated
into either group or any of the trial groups.

 The entire study population can be stratified into
subgroups according to the variable, and
individuals within each sub-group can then be
randomly allocated into study and control
groups.
 Randomization is done only after the participant
has entered the study, that is after having been
qualified for the trial and has given his informed
consent to participate in the study.

 Manipulate the study (experimental)
group by the deliberate application or
withdrawal or reduction of the suspected
causal factor.
 This manipulation creates an independent
variable whose effect is then determined
by measurement of the final outcome,
which constitutes the dependent variable.

 This implies examination of the experimental and control
group subjects at defined intervals of time, in a standard
manner, with equal intensity, under the same given
circumstances, in the same time frame till final assessment
of outcome.
 ATTRITION - some losses to follow-up are inevitable due
to factors, such as death, migration and loss of interest.
 Every effort, should be made to minimise the losses to
follow-up.

 The final step is assessment of the outcome of the trial in terms of :
(a) Positive results : that is. benefits of the experimental measure such as reduced
incidence or severity of the disease, cost to the health service or other appropriate
outcome in the study and control groups.
(b) Negative results : that is, severity and frequency of side-effects and
complications, if any, including death. Adverse effects may be missed if they are not
sought.

 The most commonly encountered experiment in health science
research, and the research strategy by which evidence of effectiveness is
measured, is the randomized, controlled, double-blind clinical trial,
commonly known as an RCT.

[A] CLINICAL TRIALS
[B] PREVENTIVE TRIALS
[C] RISK FACTOR TRIALS
[D] CESSATION EXPERIMENTS
[E] TRIAL OF ETIOLOGICALAGENTS
[F] EVALUATION OF HEALTH SERVICES

 For the most part, "clinical trials" have been concerned
with evaluating therapeutic agents, mainly drugs.
 Recent examples include –
1. Evaluation of beta-blockers in reducing cardiovascular
mortality in patient surviving the acute phase of
myocardial infarction.
2. Trials of folate treatment before conception to prevent
recurrence of neural tube defects.
3. trials of aspirin on cardiovascular mortality and beta
carotene on cancer incidence.

The intervention in a clinical trial may include:-
1. Drugs for prevention, treatment or palliation.
2. Clinical devices, such as intrauterine devices.
3. Surgical procedures, rehabilitation procedures.
4. Medical counselling.
5. Diet, exercise, change of other lifestyle habits.
6. Hospital services, e.g. integrated versus non-integrated, acute versus chronic care.
7. Risk factors.
8. Communication approaches, e.g. face-to-face communication versus pamphlets.
9. Different categories of health personnel, e.g. doctors versus nurses.
10. Treatment regimens, e.g. once-a-day dispensation versus three times a day.

 It means primary prevention.
 These trials are purported to prevent disease on an
experimental basis.
 The most frequently occurring type of preventive
trials are the trials of vaccines and chemo-
prophylactic drugs.
 For example, in 1946, the Medical Research Council
of UK conducted an extensive trial to test whooping
cough vaccine from three manufacturers in ten
separate field trials.

 A type of preventive trial is the trial of risk factors in which the investigator
intervenes to interrupt the usual sequence in the development of disease for
those individuals who have "risk factor" for developing the disease.
 For example
1. the major risk factors of coronary heart disease are elevated blood cholesterol,
smoking, hypertension and sedentary habits.

 In this type of study, an attempt is made to evaluate the termination of a habit
which is considered to be causally related to a disease.
 The familiar example is cigarette smoking and lung cancer.
 If in a randomized controlled trial, one group of cigarette smokers continue to
smoke and the other group has given up, the demonstration of a decrease in the
incidence of lung cancer in the study group greatly strengthens the hypothesis of
a causal relationship.
 A large randomized controlled trial has been mounted to study the role of
smoking cessation in the primary prevention of coronary heart disease

 One of the aims of experimental
epidemiology is to confirm or refute
an aetiological hypothesis.
 The best known example - retrolental
fibroplasia (RLF). Retrolental
fibroplasia, as a cause of blindness,
was non-existent prior to 1938. It was
originally observed and reported by
T.L. Terry. a Boston ophthalmologist
in 1942 (78). and later in many other
countries outside the USA.

 Randomized controlled trials have been extended to assess the effectiveness and
efficiency of health services. Often. choices have to be made between alternative
policies of health care delivery.
 An excellent example - controlled trials in the chemotherapy of tuberculosis in
India, which demonstrated that "domiciliary treatment" of pulmonary
tuberculosis was as effective as the more costlier "hospital or sanatorium"
treatment. The results of the study have gained international acceptance and
ushered in a new era - the era of domiciliary treatment, in the treatment of
tuberculosis.

[A] UNCONTROLLED TRIALS
[B]NATURAL EXPERIMENTS
[C]BEFORE AND AFTER COMPARISONS STUDIES

 There is room for uncontrolled trials (i.e., trials with no comparison group).
 Uncontrolled trials may be useful in evaluating whether a specific therapy appears
to have any value in a particular disease, to determine an appropriate dose, to
investigate adverse reactions, etc.
 For example – indirect epidemiological evidence that the pap test is effective in
reducing mortality from cervical cancer.

 Where experimental studies are not possible in human
populations, the epidemiologist seeks to identify
"natural circumstances" that mimic an experiment.
 For example,
1. In respect of cigarette smoking, people have
separated themselves "naturally" into two groups,
smokers and non-smokers.
2. John Snow discovery - cholera – water borne disease

These are community trials which fall into two distinct groups: -
A. Before and after comparison studies without control
B. Before and after comparison studies with control.

• These studies centre round comparing the incidence of disease before and after
introduction of a preventive measure.
• The events which took place prior to the use of the new treatment or preventive
procedure are used as a standard for comparison.
• The classic examples of "before and after comparison studies" were the
prevention of scurvy among sailors by James Lind in 1750 by providing fresh
fruit; studies on the transmission of cholera by John Snow in 1854; and more
recently, prevention of polio by Salk and Sabin vaccines.

This table gives an example of a "before and after comparison
study" in Victoria (Australia) following introduction of seat-belt
legislation for prevention of deaths and injuries caused by motor
vehicle accidents.

 In the absence of a control group, comparison between observations before and
after the use of a new treatment or procedure may be misleading.
 In such situations, the epidemiologist tries to utilize a "natural" control group
i.e., the one provided by nature or natural circumstances.
 If the preventive programme is to be applied to an entire community, he would
select another community as similar as possible, particularly with respect to
frequency and characteristics of the disease to be prevented.

 IN THIS EXAMPLE, THE EXISTENCE OF A CONTROL WITH
WHICH THE RESULTS IN VICTORIA COULD BE COMPARED
STRENGTHENS THE CONCLUSION THAT THERE WAS DEFINITE
FALL IN THE NUMBER OF DEATHS AND INJURIES IN
OCCUPANTS OF CARS AFTER THE INTRODUCTION OF
COMPULSORY SEAT-BELT LEGISLATION.

• [A] It is scientifically ideal method .
• [B] It removes large number of biases .
• [C] It build up ‘faith’in the findings of study .
• [D] It ensures temporal relationship between exposure and outcome.

• [A] It needs long time.
• [B] It has ethical issues.
• [C] It is expensive.
• [D] In many situations especially those which concern study of risk factors, one
can not randomly allocate human beings into 2 groups .

 Park K. Textbook of Preventive & Social Medicine, 22nd Edition. Jabalpur:
Banarasidas Bhanot Publishers; 2013.
 Peter S. Essentials of Preventive & Community Dentistry, 2nd Edition. New
Delhi: Arya Publishing House; 2004.
 C.M. Marya, A Textbook of Public Health Dentistry, Jaypee Brothers
Medical Pub; 1 edition, 30 March 2011.

 S.S. Hiremath, Textbook of preventive and community dentistry, Elsevier;
Second edition, 1 January 2011
 Health Research Methodology – A Guide for training in Research (1992).
WHO
 www.googleimages.com

Experimental epidemology

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