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EXPERIMENTAL EPIDEMIOLOGY Presented by: Ankita Parmar Community medicine department C.U.S.M.C


EXPERIMENTAL STUDIES Experimental studies Action, intervention or manipulation such as deliberate application or withdrawal of suspected cause or Changing one variable in causative chain in the experimental group with no change in control group


EXPERIMENTAL STUDIES Aims: Scientific Proof of risk factors Measuring the effectiveness and efficiency of health servies







Prevention of Scurvy – Orange & Lemon:

Prevention of Scurvy – Orange & Lemon

Scurvy Prevention:

Scurvy Prevention

Randomized controlled trials:

”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


”Gold standard” in epidemiological research Makes study groups comparable Prevents selection bias RCT?

Design - conduct:

Design - conduct Protocol Selecting Reference and Experimental population Randomization Intervention Follow up Analysis and interpretation


PROTOCOL Protocol specifies : Aims and objectives of study Questions to be answered Criteria for selection of study and control groups Size of the sample

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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

Selection of study population :

Selection of study population Reference (Target) population The population to whom the results of the trial is applicable.

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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 )

Reference & Study Population:

Reference & Study Population Reference Population Study Population

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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

Radomization :

Random = governed by chance Randomization = allocation of individuals to groups by chance Each sampling unit has the same chance of selection Radomization

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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

Table of Random Numbers:

Table of Random Numbers

Why randomization is important?:

Ensure comparability Avoid selection bias Why randomization is important?


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


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


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

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Non-adherence will decrease the statistical power to detect the true effect of the study intervention Strategies to enhance adherence Selection of interested/reliable study population Frequent contact with participants Monitoring adherence Self report Biochemical parameters


Assessment of outcome of the trial 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

Bias of Priene (600 - 540 BC) :

Bias of Priene ( 600 - 540 BC) Consulted by Croesus, king of Lydia, about the best way to deploy warships against the Ionians Bias wished to avoid bloodshed, so he misled Croesus, falsely advising him that the Ionians were buying horses Bias later confessed to Croesus that he had lied and that the Ionians were also building warships. Croesus was pleased about his motives and made peace with the Ionians. Bias = deviation from truth


BIAS: Subject bias Observer bias Evaluation bias



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Single – blind Subject is kept ignorant about allocated study regime Double blind Both observer and the subject are kept ignorant about allocated study regime Triple blind Observer, subject & investigator are kept ignorant about the allocation study population

Study Designs:

Study Designs Concurrent Parallel study design Cross- over type of study design

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Patients Random Assignment Exposed to specific Rx Unexposed to specific Rx COMPARE OUTCOME Concurrent Parallel study design

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Patients Random Assignment Exposed to specific Rx Unexposed to specific Rx COMPARE OUTCOME EXPOSED AND UNEXPOSED TO Rx Cross- over type of study design

Types of Randomized controlled trials:

Types of Randomized controlled trials Clinical trials Preventive trials Risk factor trials Cessation experiments Trial of etiological agents Evaluation of health services

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Clinical Trial Concerned with evaluating therapeutic agent, mainly drugs eg . Evaluation of beta-blockers in reducing cardiovascular mortality Not all clinical trials are susceptible to being blinded

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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

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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

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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

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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

Unique problemes of intervetion studies:

Ethical issues Feasibility Problems of finding sufficiently large eligible sample size Costs Expensive Unique problemes of intervetion studies


NON-RANDOMIZED CONTROL TRIAL RCT may have ethical, administrative and other problems – in such cases Non- RCT can be used. Examples : Induction of cancer by viruses have not let themselves to direct experimentation in humans. Some preventive measures can be applied only on community wide basis e.g. water fluoridation If disease frequency is low and natural history long e.g. ca. cervix

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There is No randomization in non-experimental trials so: Degree of comparability will be low Chances of spurious result higher


EXAMPLES OF NON-RANDOMIXED TRIALS Uncontrolled trials Natural experiments Before and after comparison studies:

Before and after comparison studies without control :

Before and after comparison studies without control 1970 1971 % Change Deaths 564 464 -17.7 Injuries 14620 12454 -14.8 Effect of adoption of compulsory seat-belt legislation in Victoria, Australia-1971

ii. Before and after comparison studies with control :

ii. Before and after comparison studies with control 1970 1971 %change 1.Deaths Victoria 564 464 -17.7 Other states 1426 1429 0.2 2.Injuries Victoria 14620 12454 -14.8 Other states 39980 40396 1.0

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In the evaluation of preventive measures 3 questions are generally considered: How will it benefit to community? What are the risks to the recipients? Cost in money and man power?

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