2. Experimental Studies
• Experimental studies are ones where researchers
introduce an intervention and study the effects
under the direct control of the investigator”
• The study in which an investigator manipulates or
controls one or more independent variables and
observes the effect on dependent variables.
3. Unique Features of Experiment
• Experiments provide strongest evidence about the
existence of a cause-effect relationship.
4. Aims of Experimental Epidemiology
❏ To provide “Scientific proof” of etiological or risk
factors which may permit the modification or control
of those diseases.
❏ To provide a method of measuring the effectiveness
and efficiency of health services for the prevention,
control and treatment of disease and improve the heath
of the community.
7. ”An epidemiological experiment in which
subjects in a population are randomly allocated
into groups, usually called study and control
groups to receive and not receive an
experimental preventive or therapetuic
procedure, maneuver, or interventition”
John M.Last, 2001
Randomized Controlled Trials
8. • ”Gold standard” in epidemiological research
• Makes study groups comparable
• Prevents selection bias
Randomized Controlled Trials
10. Steps Involved In Randomized Controlled Trials Are
As Follows :
1. Drawing up a protocol
2. Selecting reference and experimental
populations( Study Population)
3. Randomization
4. Intervention or Manipulation
5. Follow up
6. Assessment of outcome
11. Drawing up a protocol
• Drawing up a Protocol specifies :
Aims and objectives of study
Questions to be answered
Criteria for selection of study and control groups
Size of the sample
12. Procedures for allocation of subjects into study and
control groups
Treatment to be applied-when ,where & how
Schedules as well as responsibilities of parties
involved in the trial up to the outcome of the study
Drawing up a protocol…
13. Selecting reference and experimental
populations
• The experimental population is selected from the
reference population. The results of experimental
population if found successful, it is applied for the
reference population.
14. • Experimental population
• The actual group in which the trial is conducted
• Representive of the reference population
• Possibility for accurate follow up of information
during the trial( stable group )
16. Selection of study population
• Participants must be fully informed
- Purpose
- Procedure
• Risks
• Benefits
• Willing to participate
• Informed consent
• Screened for eligibility
• Inclusion criteria
• Exclusion criteria
17. 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 or intervention.
Radomization
18. • Random = governed by chance
• Randomization = allocation of individuals to groups
by chance
• Each sampling unit has the same chance of selection
Radomization
19. Randomization
- Heart of the control trial
- Procedure: Participants are allocated into study
and control groups
- Both groups should be alike with regards to
certain variables that might affect the outcome of
the experiment
- Best done by using table of random numbers
21. Intervene or manipulate the study group:
Experimental group
• Application, withdrawal or reduction of suspected
causal factor
e.g. drug, vaccine, habit
Control group
• no intervention, usual care, placebo
Intervention
22. Examination of experimental and control groups at
defined interval of time,
in a standard manner,
with equal intensity,
in the same time frame
until the final assesment of OUT COME
Follow-up
23. • Some losses to follow up are inevitable such as death,
migration, loss of interest- "Attrition "
• Possible reasons for non-adherence
• Developing side effects
• Forgetting to take medication
• Withdrawing consent
• Decide alternative treatment
• Health issues: treatment contraindicated
• Extent of non-adherence is related to length of study time
Attrition:
24. This is the final step of the trial. The outcome may
be positive or negative. During the assessment of the
outcome, bias is inevitable.
Positive (Benifits) and Negative (side effects etc..)
results are compared in both groups.
If there is difference, Test of Significance is applied
to find out the significance.
Assessment
BIAS ARISE FROM ERRORS OF ASSESMENT OF THE OUTCOME
30. Types of Randomized controlled trials
Clinical trials
Preventive trials
Risk factor trials
Cessation experiments
Trial of etiological agents
Evaluation of health services
31. 1. Clinical Trial
- Concerned with evaluating therapeutic agent,
mainly drugs
eg. Evaluation of beta-blockers in reducing
cardiovascular mortality
32. 2. Preventive Trials:
- Trial of primary preventive measures eg.
Vaccines
- Analysis of preventive trials must result in clear
statement about benefits to community, risk
involved and cost to health
33. 3. Risk Factor Trials:
- Investigator intervenes to interrupt the usual
sequence in the development of disease for
those individuals who have risk factor for
developing the disease
- Primary prevention of CHD using clofibrate to
lower serum cholesterol
34. 4. Cessation Experiment:
- An attempt is made to evaluate the termination
of a habit which is considered to be causally
related to disease
- Cigarette smoking and lung cancer
35. 5. Trials of Etiological Agents:
- To confirm or refute an etiological hypothesis
6. Evaluation of Health Services:
- To evaluate effectiveness and efficiency of health
services
- Domiciliary treatment of Pulmonary Tuberculosis was as
effective as the more costlier hospital or sanatorium
treatment
36. • Ethical issues
• Feasibility
• Problems of finding sufficiently large eligible
sample size
• Costs
• Expensive
Unique problemes of intervetion studies
37.
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41.
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43.
44.
45. APPLICATION OF
EPIDEMIOLOGY
To describe the spectrum of disease.
To describe the natural history of disease.
To formulate Community Diagnosis
To Describe the clinical picture of a disease
To Identify the factors that increase or decrease of disease
To Identify precursor of disease & syndrome
Test the efficacy of intervention strategies
Investigation the epidemic of unknown disease
Evaluate public health programme
Elucidate the mechanism of disease transmission
