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USING A BALANCING PROCEDURE IN MULTICENTER CLINICAL TRIALS

Simulation of Patient Allocation Based on a Trial of Ventilation Tubes for Otitis Media With Effusion in Infants

Published online by Cambridge University Press:  04 May 2001

Maroeska M. Rovers ,
Huub Straatman ,
Gerhard A. Zielhuis ,
Koen Ingels  and
Gert-Jan van der Wilt
Maroeska M. Rovers
Affiliation:
University Hospital Nijmegen
Huub Straatman
Affiliation:
University of Nijmegen
Gerhard A. Zielhuis
Affiliation:
University of Nijmegen
Koen Ingels
Affiliation:
University Hospital Nijmegen
Gert-Jan van der Wilt
Affiliation:
University of Nijmegen
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Abstract

Objective: A basic issue in randomized controlled trials (RCTs) is whether we can safely assume comparability between groups at baseline with respect to all potentially important prognostic factors. In other words, did randomization work sufficiently well? In small trials balanced allocation procedures are employed, whereas in large-scale trials simple randomization will do. The question is: When should balancing be considered?

Methods: We performed a simulation study in which we varied the number of categories in the prognostic factors and the number of patients.

Results: Simulation showed that, in all instances, a balancing procedure almost always led to perfect or almost perfect balance, while the imbalance with simple randomization was larger. To study the effect of balanced and random allocation on subgroup analyses in our OME trial, we compared the quotient of the width of the confidence intervals (CI). The widest CI in random allocation over the 13 hospitals was on average 13% wider than in balanced allocation.

Conclusion: Investigators should always consider balanced allocation, especially in categories with a low number of patients and when subgroup analysis over many categories is requested.

Keywords

Randomized controlled trialsBalanced allocationPrognostic factorsImbalance
Type
RESEARCH NOTES
Information
International Journal of Technology Assessment in Health Care , Volume 16 , Issue 1 , January 2000 , pp. 276 - 281
Copyright
© 2000 Cambridge University Press

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