Abstract
Randomization of patients to different therapy groups has been established to a gold standard in clinical trials. But pre-stratification of randomization has been discussed as a controversial issue in this context. To support investigator’s decision concerning stratification in the phase of planning a trial we investigated the impact of stratification with respect to the risk of prognostic imbalance between treatment groups by a simulation approach. We give a comprehensive overview of the risk for pre-defined imbalances, several trial sizes and prevalence of a prognostic factor, comparing stratified vs. unstratified randomization.We quantified the maximum risk of a prognostic imbalance due to randomization of 59 % (complete randomization CR, N = 30, prevalence of a prognostic factor 50 %). For type I error we calculated a maximum of 32 % (permuted-block randomization PBR(B), N = 100, average success rate 50 %) for a clinically relevant difference, and about 5 % for a statistically significant difference in trials with N = 100 or 400 patients. Stratification can be helpful to reduce this risk by up to 16 percentage points (pps) for clinical differences in the case of a large average success rate of 50 %, and large differences between the strata (10 % vs. 90 %) in small trials of N = 100. For statistical differences, however, the impact of stratification is rather negligible.
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References
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Feinstein, A.R., Landis, J.R.: The role of prognostic stratification in preventing the bias permitted by random allocation of treatment. J. Chronic Dis. 29(4), 277–284 (1976)
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© 2014 Springer Science+Business Media New York
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Glass, A., Kundt, G. (2014). Potential Advantages and Disadvantages of Stratification in Methods of Randomization. In: Melas, V., Mignani, S., Monari, P., Salmaso, L. (eds) Topics in Statistical Simulation. Springer Proceedings in Mathematics & Statistics, vol 114. Springer, New York, NY. https://doi.org/10.1007/978-1-4939-2104-1_23
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DOI: https://doi.org/10.1007/978-1-4939-2104-1_23
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