7. experimental epidemiology

Experimental epidemiology overview

1. Experimental Epidemiology Maj Dr Naveen Phuyal MBBS, MD

2. Randomized Control Trial Maj Dr Naveen Phuyal MBBS, MD

3. The ideal design to use in epidemiological research settings is an experimental design. Experimental epidemiology is a model epidemiological method.

4. 1920s: Experimental epidemiology meant study of epidemics among colonies of experimental animals such as rats and mice.

5. How does it differ from cohort studies? The conditions in which the studies are carried out are under direct control of the investigator. Involves some action, intervention or manipulation such as deliberate application or withdrawal in an experimental group and a control group Observes and compares the outcome of experiment in both groups

6. Aims of experimental studies To provide scientific proof of etiological factors which may permit modification or control of disease To provide a method of measuring the effectiveness and efficiency of health services for the prevention, control and treatment of disease and improve the health of the community

7. Experimental studies have all advantages and disadvantages of cohort studies plus Costlier Ethical issues Feasibility

8. Experimental Studies ANIMAL STUDIES HUMAN EXPERIMENTS

9. Animal Studies Animals have played important role in men’s quest for knowledge about himself. Animal studies have contributed to all branches of medicine. Application To confirm etiological hypothesis and study pathogenic phenomena Testing efficacy of preventive and therapeutic measures such as vaccines or drugs Completing the natural history of disease

10. Animal Studies A dvantage Can be bred easily Multiply rapidly Genetic experiments Disadvantage Not all human disease can be reproduced in animals All conclusions drawn may not strictly apply to humans

11. Human Experiments Human experiments will always be needed to investigate disease etiology and evaluate the preventive and therapeutic measures

12. All who drink of this treatment recover in a short time , Except those whom it does not help, who all die , It is obvious, therefore, that it fails only in incurable cases . Galen [1] (129–c. 199 ce )

13. Sir Francis Galton 1883 It was asserted by some that men possess the faculty of obtaining results over which they have little or no direct personal control, by means of devout and earnest prayer, while others doubt the truth of this assertion. The question regards a matter of fact, that has to be determined by observation and not by authority; and it is one that appears to be a very suitable topic for statistical inquiry. … Are prayers answered or are they not? … Do sick persons, who pray or are prayed for, recover on the average more rapidly than others?

14. Are prayers answered or are they not? 1965 : Joyce and Welldon double blind randomized trial of efficacy of prayer 1988 : randomized double blind control trial in CCU

15. Ambroise Pare , 1537 Unplanned trial At length my oil lacked and I was constrained to apply in its place a digestive made of yolks of eggs, oil of roses and turpentine. That night I could not sleep at my ease, fearing that by lack of cauterization I would find the wounded upon which I had not used the said oil, dead from the poison . I raised myself early to visit them, when beyond my hope I found those to whom I had applied the digestive medicament feeling but little pain, their wounds neither swollen nor inflamed, and having slept through the night. The others to whom I had applied the boiling oil were feverish with much pain and swelling about their wounds. Then I determined never again to burn thus so cruelly the poor wounded.

16. James Lind 1747, Planned trial I took 12 patients in the scurvy on board the Salisbury at sea. The cases were as similar as I could have them … they lay together in one place and had one diet common to them all .

17. Two of these were ordered a quart of cider per day. … Two others took 25 gutts of elixir vitriol. … Two others took two spoonfuls of vinegar. … Two were put under a course of sea water. … Two others had two oranges and one lemon given them each day. … Two others took the bigness of nutmeg . The most sudden and visible good effects were perceived from the use of oranges and lemons, one of those who had taken them being at the end of 6 days fit for duty. … The other … was appointed nurse to the rest of the sick.

18. Types of experimental studies Clinical (therapeutic) trial- patient suffering from disease Field trial (preventive trial)- healthy individuals in the community Community intervention trial- cluster of human beings Health service evaluation trial Risk factor trial Cessation experiments

19. Randomized Control Trial Maj Dr Naveen Phuyal MBBS, MD

20. NON RANDOMIZED TRIALS

21. Ethical, administrative and other reasons for which RCT not possible Direct experimentation not possible : smoking and Lung CA Some preventive measure can be only be applicable to small groups in a community ( flouridation ) When disease frequency is low and natural history is long ( Cervical Ca )

22. A crude approach Degree of comparability is low Chances of spurious results higher Validity becomes extra statistical judgment Vital decisions in public health have been made by non-experimental studies

23. Non-randomized trials Uncontrolled trials (trials with no comparison groups). Eg . Pap smear test reduces mortality from Cx CA Natural experiments cigerrete smoking: smokers vs non smokers Natural disasters, atomic bombings, mogrants , social groups, “The Great Experiment” Before and after comparison studies ( eg . James Lind and scurvy) Using a control group Without a control group