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Simple procedures for blinded sample size adjustment that do not affect the type I error rate.

Kieser, Meinhard; and Friede, Tim (2003) Simple procedures for blinded sample size adjustment that do not affect the type I error rate. Statistics in Medicine, 22 (23). pp. 2571-2581. ISSN 1097-0258

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For normally distributed data, determination of the appropriate sample size requires a knowledge of the variance. Because of the uncertainty in the planning phase, two-stage procedures are attractive where the variance is reestimated from a subsample and the sample size is adjusted if necessary. From a regulatory viewpoint, preserving blindness and maintaining the ability to calculate or control the type I error rate are essential. Recently, a number of proposals have been made for sample size adjustment procedures in the t-test situation. Unfortunately, none of these methods satisfy both these requirements. We show through analytical computations that the type I error rate of the t-test is not affected if simple blind variance estimators are used for sample size recalculation. Furthermore, the results for the expected power of the procedures demonstrate that the methods are effective in ensuring the desired power even under initial misspecification of the variance. A method is discussed that can be applied in a more general setting and that assumes analysis with a permutation test. This procedure maintains the significance level for any design situation and arbitrary blind sample size recalculation strategy.

Item Type: Article
Journal or Publication Title: Statistics in Medicine
Uncontrolled Keywords: clinical trial • internal pilot study • sample size adjustment • two-stage design
Subjects: Q Science > QA Mathematics
Departments: Faculty of Science and Technology > Mathematics and Statistics
ID Code: 10005
Deposited By: Mrs Yaling Zhang
Deposited On: 25 Jun 2008 16:43
Refereed?: Yes
Published?: Published
Last Modified: 24 Jun 2016 01:02
Identification Number:

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