EXPERIMENTAL EPIDEMIOLOGY

• INTERVENTION STUDY

• EXPERIMENTAL STUDY

• RANDOMIZED CONTROLLED TRIALS

• In which experiment or trials are made and results are watched.

EXPERIMENTAL STUDIES

• Experimental studies are similar in approach to cohort studies excepting that the conditions in which study is carried out are under direct control of the investigator.

EXPERIMENTAL STUDIES

• Involve some action, intervention or manipulation:

– Application of a drug, vaccine

– Withdrawal of certain factor

– Changing one variable in exp. group and no change in control group & then observing &comparing the out come of two groups

EXPERIMENTAL STUDIES

• The researcher manipulates a situation and measures the effects of the manipulation. Usually two groups are compared, one in which the intervention takes place (treatment with a certain drug) and the other remains untouched (treatment with a placebo).

AIMS OF EXPERIMENTAL STUDIES

• To provide scientific proof of aetiological factors which may permit modifications or control of those diseases.

• To provide a method of measuring the effectiveness and efficiency of health services for prevention, control and treatment of diseases and improve the health of the community.

ANIMAL STUDIES

• Contributed to our knowledge

• Reproduction of human diseases in animals to confirm aetiological hypothesis, mechanism of disease occurrence

• Testing the efficacy of preventive and therapeutic measures e.g. vaccine, drugs

• Completing the natural history of diseases

ANIMAL STUDIES

• ADVANTAGES:– animals can be bred in laboratories and manipulated

easily a/c to wishes of the investigator– Animals multiply rapidly and enable the investigator to

carry out experiments

• LIMITATIONS:– Not all human diseases can be reproduced in animals– Conclusions derived from animal experiments may

not be applicable to human beings.

EXPERIMENTAL STUDIES

• Most incisive approach to scientific problem, the only study that can prove causation.

• Ethical problems, Logistic considerations• Benefits of the study must be weighed

against risks• Persons involved in research must be fully

informed about all possible consequences of the experiment.

Steps in Experimental Study

• 1. Drawing up of a protocol

• 2. Selection of reference and experimental population

• 3. Randomization

• 4. Manipulation or intervention

• 5. Follow up

• 6. Assessment of outcome

1.Drawing up of a protocol

• To specify aims and objectives of the study• Questions to be answered• Criteria for the selection of study and control

group• Size of the sample• Procedures for allocation of subjects into study

and control groups• Action, treatment to be applied• Schedule and evaluation of outcome of the

study• Protocol must be adhered throughout the study.

2. Selection of reference & experimental population

• Reference or target population– Population in which findings of trial are expected to be

applicable

• Experimental or study population– Derived from reference population– Randomly chosen group from reference population– Chose a stable population

• Informed consent• Representative of the population• Eligible for the trial

3. RANDOMIZATION

• A statistical procedure by which participants are allocated into groups i.e. study and control to receive or not to receive a preventive, therapeutic procedure or intervention.

• Each subject is given an equal opportunity/chance of being assigned to either group and blindly selecting the numbers for each group.

• Randomization allows comparability and eliminates errors.

Manipulation

• Intervene or manipulate the study group– Application of – Withdrawal of– Reduction of suspected causal factor

• Independent variable whose effect is determined by measurement of final outcome that constitutes the dependent variable.

Follow up

• Examination of control and study groups at regular intervals – Standard manner– Equal intensity– Same conditions

• Duration must be sufficient to demonstrate a significant difference

• Follow up may be short or long• Minimize the losses to follow up.

Assessment

• Positive results

• Negative results

• Comparison of results in both groups

• Differences are tested statistically

• ERRORS– Subject variation– Observer variation– Bias in evaluation

BLINDING

• The concealment of group assignment from the knowledge of the patients and/ or investigators in a clinical trial.

• Blinding eliminates possibility

– The knowledge of assignment may affect patient response to treatment

– The Investigator’s behaviour that may affect outcome

SINGLE BLIND TRIAL

• The participant is not aware whether he belongs to a study or control group

• Knowledge of group assignment is with held only from patients.

DOUBLE BLIND TRIAL

• The trial is so planned that neither the doctor nor the participant is aware of the group allocation and treatment received

• Knowledge of group assignment is with held from patients and investigators

TRIPLE BLIND TRIAL

• The participant, the Investigator and the person analyzing data are all blind.

• Knowledge of assignment is with held from patients, investigators and analyst.

Experimental study

Quasi-experimental study design

Study Group

Before Intervention study group

after

Compare

Control group

Before control group

after

SELECTION OF STUDY DESIGN

• Type of information you want to obtain • Devise strategies to enable to obtain that

information. • The selection of an appropriate study design

depends on:– The state of knowledge about the problem– The nature of the problem and its environment.– The resources available for the research– Objectives of the study.

CASE

• A person who has a particular disease, health disorder or condition which meets a set of diagnostic criteria to be regarded as a case of disease and for surveillance and outbreak investigation purpose.