10class.wk3 - PubH 5462 Clinical Trials: Readings for Week...

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PubH 5462 Clinical Trials: Readings for Week 3 1. Fundamentals of Clinical Trials , Chapter 5. Supplemental Reading/References 1. Lachin JM, Matts JP, Wei LJ. Randomization in clinical trials: conclusions and recommendations. Cont Clinical Trials , 9:365-374, 1988. 2. Pocock SJ, Lagakos SW. Practical experience of randomization in cancer trials: an international survey. Br. J. Cancer , 46, 368-375, 1982. 3. Schulz KF. Subverting randomization in controlled trials. JAMA 274:1456-1458, 1995. 4. Zelen M. A new design for randomized clinical trials. NEJM , 300: 1242-1245, 1979. 5. Clinical Trials: A Practical Approach , Chapters 5 and 7. 6. Clinical Trials, Design, Conduct and Analysis , Chapter 10. 1
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It is extremely important to implement the randomization scheme in a manner that ensures that assignments are concealed until the time of allocation. Otherwise, selection bias may be introduced. Recall, eliminating selection bias is a major reason randomized studies are carried out. Friedman, Furberg, and DeMets refer to implementation plans as the "mechanics of randomization" (see pages 74-75). The Randomization Schedule (def.) - A list showing the order in which subjects are to be assigned to the different treatment groups. General Guidelines : 1. If more than one clinic is involved in the study a separate randomization schedule should be prepared for each clinic to avoid chance imbalances between treatment groups within clinics. 2. The schedule should be prepared beforehand (by a statistician usually) by a method which is reproducible. The investigator(s) seeing patients should not be involved in its preparation or see it after it has been prepared. Schedules should be maintained in secure files (computer or otherwise). The randomization procedure should be audited by an outside group at the beginning of the study. 3. The ultimate purpose is to devise a schedule which will achieve an unbiased distribution on the average and one that will assign treatments with some pre- specified frequency. Once developed, the outcome of the assignment should not be changed by the investigator or statistician. 4. A schedule should be devised for which the investigator cannot easily guess the next assignment. Developing a schedule which minimizes the chance of a selection bias is extremely important in non-blind studies e.g. MRFIT where the investigator is aware of the previous treatment assignments. See the article by Schulz in JAMA in 1995 for personal accounts of how randomization schemes have been deciphered. A letter in response to the article by Schulz et al. argues for using "watertight" methods to implement randomization schemes to ensure that future assignments cannot be determined, and for publishing the details of randomization schemes (Martyn C, Lancet , 347:70, 1996). 2
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10class.wk3 - PubH 5462 Clinical Trials: Readings for Week...

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