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Randomization in medical research
This document discusses randomization in medical research. It defines randomization as the allocation of individuals to intervention or control groups in a clinical trial by chance. Randomization avoids selection bias and balances both known and unknown confounding factors between groups. Participants, communities, or locations can be randomized. Simple, permuted block, stratified, and adaptive randomization methods are described. Threats to randomization include non-adherence to the randomization protocol and lack of treatment equipoise. Maintaining the integrity of randomization is important for establishing causality in medical research.
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Randomization in medical research
- 1. Randomization in medical research MPHCourse - Epidemiology Module Dr. Vignesh L, M.D. (AIIMS, New Delhi) Senior Resident Department of Preventive & Social Medicine JIPMER, Puducherry
- 2. Outline • What israndom & randomization? • Why to randomize? • Whom and what to randomize? • How to randomize? • Threats to randomization • References and further reading
- 3. Source: The Lancet2002; 359:57-61 (DOI:10.1016/S0140-6736(02)07283-5)
- 7. Random • No specificpattern • Un predictable • Completely guided by a ‘known’ chance
- 8. Randomization Allocation of individualsto intervention or control of a clinical trial by chance • Each possible assignment has a known chance of being selected • Treatment assignment is unpredictable
- 9. Why to Randomize? •Avoids selection bias • Balances confounding factors between both the groups – Known and unknown factors • Allows to perform statistical tests for establishing causality
- 10. What to Randomize? •Participants / Individual – Classical RCT • Community / locality – Community trial or Cluster randomized trials
- 11. How (not) toRandomize? • Birth date • Hospital record number • Hospital room number • Day of visiting the hospital
- 12. How to Randomize? •Simple randomization • Permuted block randomization • Stratified randomization • Adaptive randomization
- 13. Block randomization • Everyblock of X new participants is randomly and equally allocated to treatment arms A & B • Block size 4 – 6 possibilities ABBB AABB AAAB BAAA BBAA BBBA Advantage • Equal assignment Disadvantage • If block size is known, last participant assignment can be predicted – random/unknown block size • Imbalance in critical variables
- 14. Stratified randomization • Importantvariables that can affect the outcome are stratified and randomization done separately between these strata • E.g., Study site in multi-site trial Advantage • Balance of critical variables achieved Disadvantage • Can’t use too many variables for strata ( < 4 )
- 15. Threats to randomization •Per-protocol analysis Versus Intention-to-treat analysis • Equipoise and randomization
- 16. References • Leon Gordis– Epidemiology 6th Edition • John Last – A Dictionary of Epidemiology • Introduction to the Principles and Practice of Clinical Research (IPPCR) – Issues in Randomization: Video in Youtube - https://www.youtube.com/watch?v=UgFXLk7i46c&ab_channel=NIHVideo Cast Topics for further reading: • Adaptive randomization
- 17.