EXPERIMENTAL EPIDEMIOLOGY
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Experimental epidemiology aims to provide scientific proof of disease causes and evaluate health interventions. Randomized controlled trials are the gold standard for testing hypotheses. Key elements of RCTs include being prospective, having an intervention and control group, and being randomized and blinded. RCTs involve developing a protocol, selecting and randomizing populations, implementing interventions, following up on outcomes, and assessing results by comparing intervention and control groups. Non-randomized trials may also be used when RCTs are not feasible.
EXPERIMENTAL EPIDEMIOLOGY
- 4. INTRODUCTION An experiment is: ļ§ the final or definitive step in the research process, ļ§ a mechanism for confirming or rejecting the validity of ideas, assumptions and hypothesis. The Randomized Controlled Trial (RCT) is the most scientifically rigorous method of hypothesis testing available GOLD STANDARD TRIAL evaluating the effectiveness of interventions
- 5. AIMS To provide: ļ "scientific proof" of etiological factors. ļ A method of measuring the effectiveness and efficiency of health services. EXPERIMENTAL EPIDEMIOLOGY ANIMAL STUDIES HUMAN EXPERIMENTS
- 6. HUMAN EXPERIMENTS Human experiments will always be needed to investigate disease aetiology and to evaluate the preventive and therapeutic measures. History: James Lind (1747): Study on scurvy
- 8. CLASSIFICATION Randomized controlled trials ā¢ those involving a process of random allocation Non ā randomized trials ā¢ those departing from strict randomization for practical purposes, but in such a manner that non- randomization does not seriously affect the theoretical basis of conclusions.
- 10. Essential elements of a clinical trial 1. Prospective Subjects followed forward 2. Intervention Prophylactic, diagnostic or therapeutic 3. Control Compared to intervention group 4. Randomized Equality of baseline characteristics 5. Blinded Systematic bias
- 11. Structure of a clinical trial
- 12. Steps in clinical trial 1. Drawing up a protocol 2. Selecting reference and experimental populations 3. Randomization 4. Manipulation or intervention 5. Follow-up 6. Assessment of outcome
- 13. THE PROTOCOL ļ¼The aims and objectives ļ¼Questions to be answered ļ¼Criteria for the selection of study and control groups ļ¼Size of the sample, ļ¼Procedures for allocation of subjects ļ¼Treatments to be applied ļ¼Standardization of working procedures ļ¼Schedules ļ¼Responsibilities of the parties
- 14. Clinical trial question Type of research question determines the trial design For a research question addressing an intervention: P ā¢ POPULATION I ā¢ INTERVENTION C ā¢ COMPARISON O ā¢ OUTCOME T ā¢ TIME
- 15. For adult patients, will the use of a powered toothbrush, compared to a manual toothbrush, result in reduction in plaque and/or gingivitis? P I C O TRY THIS
- 16. SELECTING REFERENCE AND EXPERIMENTAL POPULATIONS REFERENCE OR TARGET POPULATION: ļ¶It is the population to which the findings of the trial, if found successful, are expected to be applicable. EXPERIMENTAL OR STUDY POPULATION ļ¶The study population is derived from the reference population, on which the study is conducted..
- 17. RANDOMIZATION Of a clinical trial
- 20. PREDICTABILITY The critical element of randomization is the unpredictability of the next assignment
- 21. RANDOMIZATION Randomization is a statistical procedure by which the participants are allocated into groups usually called āstudyā and ācontrolā groups. Elimination of āselection biasā Three common randomization schemes ļSimple Randomization ļStratified Randomization ļCluster Randomization
- 22. Randomization Objective of randomization ļ§ Everyone in the study has an equal probability of being offered each intervention ļ§ All prognostic variables, known and unknown, have an equal distribution in the treatment groups in the long run
- 23. Methods of randomization Simple randomization
- 26. MANIPULATION The next step is to intervene or manipulate the study (experimental) group by the deliberate application or withdrawal or reduction of the suspected causal factor or drug or treatment.
- 27. FOLLOW-UP This implies examination of the experimental and control groups: ļat defined intervals of time, ļin a standard manner, with equal intensity, ļunder the same given circumstances, ļin the same time frame till final assessment of outcome.
- 28. ASSESSMENT The final step is assessment of the outcome of the trial in terms of- ļ¶Positive results- reduced incidence or severity of the disease, cost to the health service or other appropriate outcome. ļ¶Negative results- severity and frequency of side-effects and complications. The incidence of positive/negative results is rigorously compared in both the groups.
- 29. BIAS IN CLINICAL TRIALS Bias may arise from errors of assessment of the outcome due to human element- ļ§SUBJECT VARIATION ļ§OBSERVER BIAS ļ§EVALUATION BIAS
- 30. BLINDING/MASKING It is the procedure of keeping the knowledge of intervention assignment away from those directly involved in the trial. Ensures that the outcome is assessed objectively. Can be done in three ways- ļSingle Blind Trial ļDouble Blind Trial ļTriple Blind Trial
- 32. BASIC DESIGNS OF CLINICAL TRIALS ļ±Basic two-arm parallel design ļ±Cross over design ļ±Factorial design
- 34. PHASES OF CLINICAL TRIAL
- 35. Types of clinical trials ļEffectiveness: Examine the outcomes of interventions under circumstances that more closely approximate the real world ļEfficacy: Investigates the benefits of an intervention under ideal and highly controlled conditions
- 36. Other types of clinical trials . . . ļ§Preventive trials ļ§Risk factor trials ļ§Cessation experiments ļ§Evaluation of health services ļ§Field trials ļ§Community trials
- 37. NON-RANDOMIZED TRIALS ā¢ It is undertaken when: ā¢ Not feasible to conduct RCT ā¢ Secondly, some preventive measures can be applied only to groups or on a community-wide basis. ā¢ Thirdly when natural history of disease is long
- 38. Examples of non-randomized trials ļUncontrolled trials ļNatural experiments ļBefore and after studies
- 39. ADVANTAGES ā¢Safety: relatively few individuals exposed to unpredicted risks in untried interventions. ā¢Vigour : capable of critical tests of limits of applicability. ā¢Precision: theorized causal factor can be defined and limited exposure of test factor under control of researcher. ā¢Efficiency: relatively few observations needed to refute some hypothesis. ā¢Assumptions: random allotment of treatments is assured by the design.
- 40. DISADVANTAGES ļ¼Impracticality: inborn attributes cannot be manipulated. ļ¼Predicted risk of intervention is great. Long term observation is difficult. Large number of subjects needs to detect small differences. ļ¼Reductionism: focus on one independent variable excludes others from attention. ļ¼Representativeness: difficult to recruit a truly random sample from āuniverseā. ļ¼Expense: relatively great in staff and logistics ļ¼Public acceptance: undue suspicion of outcomes.
- 41. Summary ļHierarchy of evidence ļAims of experimental epidemiology ļClassification of experimental studies ļRandomized controlled trials 1. Structure 2. Steps 3. Blinding 4. Basic designs 5. Phases ļNon-randomized trials ļAdvantages ļDisadvantages
- 42. References and suggested reading ļPARK K. PARKāS TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICINE. 21st ed. Jabalpur: Banarsidas Bhanot; 2011. ļSoben Peter. Essentials of Preventive and Community Dentistry. 4th ed. ļKendall JM. Designing a research project: randomised controlled trials and their principles. Emerg Med J. 2003 Mar 1;20(2):164ā8.