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Experimental Studies. Types of Experimental Studies Multiple experimental groups Blinds single, double, triple.

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Presentation on theme: "Experimental Studies. Types of Experimental Studies Multiple experimental groups Blinds single, double, triple."— Presentation transcript:

1 Experimental Studies

2 Types of Experimental Studies Multiple experimental groups Blinds single, double, triple

3 Public Health & Clinical Objectives Modify natural history of disease and express disease prognosis Prevent or delay death or disability Improve health of patient or population Need to use best preventive or therapeutic measures Randomized trials are ideal design to evaluate effectiveness and side effects of new forms of intervention

4 Historical Perspectives Sir Francis Galton (1883) - ruminated over the influence of prayer Joyce and Welldon (1965) found no benefit of prayer R. C. Byrd (1988) - suggested positive benefits Washington Post Parade article (2003) - also suggested positive benefits

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6 Recent Perspectives Effect of: coffee on CHD carotene on cancers hormonal therapy on breast cancer drug-lowering cholesterol on CHD

7 Randomized Trials Historically, were done accidentally, in other words, “unplanned trials” Ambroise Pare ( ) discovered new treatment for war wounds when original therapy was unavailable James Lind (1747) studying scurvy Subjects assigned to groups using a non-biased procedure

8 Design of a Randomized Clinical Trial

9 Selection of Subjects Well-designed Eliminate subjectivity Promote reliability Replicable, as with laboratory experiments Accurate

10 Selection of Subjects: Studies without Comparison Question: If we administer a drug and the patient improves, can we attribute the improvement to the administration of that drug? Answer: Results can always be improved by omitting controls. - Prof. Hugo Muensch Harvard University

11 Selection of Subjects: Studies with Comparison Historical controls (comparison group from past) Data must be abstracted from records not kept for research purposes Differences may be due to quality of the data May not be able to substantiate differences Can be useful for drugs developed against fatal diseases

12 Simultaneous Non-Randomized Controls May introduce bias Example - BCG vaccination study in NYC in 1975 Investigators introduced selection bias in the experimental group and controls A change in the study design that eliminated selection bias, although still not randomized, also eliminated differences observed in final results Selection of Subjects: Studies with Comparison (cont.)

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15 Best approach Uses tables of random numbers Must still eliminate physician bias Can achieve non-predictability Selection of Subjects (cont.): Randomization

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17 Effect of Comparability Not Randomized Randomized

18 Selection of Subjects (cont.): Stratified Randomization Useful when concerned that certain variables may affect the outcome For example, when the prognosis may be much worse for older patients Want two treatment groups to be comparable in terms of the variables of concern Initially stratify (layer) the study population according to each variable of concern and then randomize participants to treatment groups within each stratum

19 Selection of Subjects (cont.): Stratified Randomization

20 Data Collection on Subjects: Potential Variables Treatment: that was assigned that was received Outcome Explicit criteria required Comparable measurements required Prognostic Profile at Entry If risk factors for a bad outcome are known, assure that treatment groups are reasonably similar for these factors Data for prognostic factors obtained upon enrollment in study Masking (Blinding)

21 Data Collection on Subjects (cont.): Masking (Blinding) Attempt to eliminate biases & preconceptions Single-blind Subject masking Use of placebo Double-blind Subject masking and researcher masking Data collectors and data analysts Triple-blind Subject masking, researcher masking and study sponsor masking


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