Experimental epidemiology involves intervention studies where conditions are controlled by the investigator, allowing for assessments on the outcomes of disease interventions. Key types include randomized controlled trials (RCTs), non-randomized trials, field trials, and community trials, each with specific protocols and objectives. Potential biases in trial outcomes can be mitigated through blinding methods, ensuring accurate evaluation of interventions and their effects on health.

1. Experimental Epidemiology

2. INTRODUCTION
 Experimental studies (ES)= intervention studies
 Similar to cohort studies except:
 Conditions of study under direct control of investigator.
 Involve:
 Action
 Intervention
 Manipulation
 E.g. deliberate application or withdrawal of suspected cause in exp grp
with no change in control grp.....compare outcome.
Have all advantages and disadvantages of cohort studies plus 3 more: cost,
ethics & feasibility.

3. Types of experimental studies:
1. Randomized controlled trials
 Random allocation of subjects
2. Non-randomized or non-experimental trials
No strict randomization for practical
purposes, but without affecting theoretical
basis of conclusions.
a. Field trials
b. Community trials

4. 1. RANDOMIZED CONTROL TRIALS (RCT)
 RCT s – experiments to study new preventive or therapeutic interventions.
 Subjects in a population allocated randomly to groups (treatment & control).
 Ensures similar group composition.
 Results assessed by comparing outcome in the two groups.
 Outcome varies:
 Development of new disease
 Recovery from established disease.

5. Design of a randomized controlled trial

6. Basic Steps in Conducting RCTs
1. Drawing up a protocol
2. Selecting study and target populations
3. Randomization
4. Manipulation or intervention
5. Follow-up
6. Assessment of outcome

7. 1. The Protocol
Protocol specifies:
 Aims and objectives
 Questions to be answered
 Criteria for selection of study and control grp
 Treatment to be applied, when, where, how, to who.
 Standardization of procedures
 Schedules and responsibilities
 Plan for pilot study

8. 2. Selection of Target and Study Population
a) Target population = the pop to which the findings of
trial will be applicable or generalizable.
b) Study population = the actual population that
participates in the experimental study.
Randomly selected from target pop.
should be stable
Should be representative of target population.
Should be eligible for the trial.

9. 3. Randomization
 Is the allocation of participants into study and control
groups.
 Attempts to eliminate bias and allow comparability.
 Ensures that researcher has no control over allocation of
participants to study groups
 Eliminates selection bias.
RCT vs. Analytical Studies
 Analytical studies: there’s no randomization because
differentiation into diseased and not diseased is done.

10. 4. Manipulation
 Intervention/manipulation
5. Follow-up
 Examination of subjects:
 At defined intervals of time
 In a standard manner
 With equal intensity
 In the same time frame
 Attrition = losses to follow-up
 Deaths
 Migration
 Loss of interest

11. 6. Assessment
 Assess outcome in terms of:
a) Positive results
 Benefits of experiment measured as e.g. reduced incidence or severity of disease
b) Negative results
 Severity & frequency of side-effects and complications.
 Incidence of +ve & -ve results compared and tested for statistical
significance.

12. Sources of Errors in Assessment of Outcome:
I. Subject variation
 Participants subjectively report improvement if they know they are receiving a new
form of treatment.
II. Observer bias
 Investigator measuring outcome influenced if he knows before hand the particular
treatment to which the patient has been subjected.
III. Bias in evaluation
 Investigator subconsciously gives a favorable report of outcome of trial.
Randomization cannot guard against such biases.

13. Solution to these biases = BLINDING
I. Single blind trial
 Participant is not aware whether he’s in intervention or control group.
 E.g. use of placebo drug.
II. Double blind trial
 Neither participant nor doctor is aware of group of allocation and
treatment received.
III. Triple blind trial
 The participant, the investigator and the person analyzing the data
are all “blind”.

14. TYPES OF RANDOMIZED CONTROLLED TRIALS
1. Clinical trials
 Evaluating therapeutic agents (drugs).
2. Preventive trials
 Trials of primary preventive measures.
 E.g. trials of vaccines and chemo-prophylactic drugs.
3. Risk factor trials
 Investigator interrupts the usual sequence in development of disease
for individuals who have the risk factor.
 E.g. major risk factors of coronary heart disease include elevated
cholesterol levels, smoking….
 Possibilities of intervention include reduction in blood cholesterol ,
the cessation of smoking….

15. Field Trials
 Involve people who are disease free but presumed to be at risk.
 Data collection takes place in the field among non-institutionalized
people in general population.
 Purpose is to prevent occurrence of disease.
 Involve major logistical and financial considerations.
 E.g. stalk vaccine for poliomyelitis involving > 1 million children.

17. Community Trials
 The treatment groups are communities rather than individuals.
 Appropriate for diseases that have origins in social conditions.
 Intervention directed at group behaviour as well as at individuals.
 E.g. human waste disposal practices to control worm infections.
Limitations:
 Only a small number of communities can be included.
 Random allocation of communities is not practical.
 Other methods/tools required to ensure that any difference found between
communities at the end of the study can be attributed to the intervention
rather than inherent differences.

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