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Reference: Takashi Kikuchi, (2011). A Bayesian cost-benefit approach to sample size determination and evaluation in clinical trials. DPhil. University of Oxford.Citable link to this page:


A Bayesian cost-benefit approach to sample size determination and evaluation in clinical trials

Abstract: Current practice for sample size computations in clinical trials is largely based on frequentist or classical methods. These methods have the drawback of requiring a point estimate of the variance of treatment effect and are based on arbitrary settings of type I and II errors. They also do not directly address the question of achieving the best balance between the costs of thetrial and the possible benefits by using a new medical treatment, and fail to consider the important fact that the number of users depends on evidence for improvement compared with the current treatment.A novel Bayesian approach, Behavioral Bayes (or BeBay for short) (Gittins and Pezeshk, 2000a,b, 2002a,b; Pezeshk, 2003), assumes that the number of patients switching to the new treatment depends on the strength of the evidencewhich is provided by clinical trials, and takes a value between zero and the number of potential patients in the country. The better a new treatment, the more patients switch to it and the more the resulting benefit. The modeldefines the optimal sample size to be the sample size that maximises the expected net benefit resulting from a clinical trial. Gittins and Pezeshk use a simple form of benefit function for paired comparisons between two medical treatments and assume that the variance of the efficacy is known.The research in this thesis generalises these original conditions by introducing a logistic benefit function to take account of differences in efficacy and safetybetween two drugs. The model is also extended to the more general cases of unpaired comparisons and unknown variance. The expected net benefit defined by Gittins and Pezeshk is based on the efficacy of the new drug only.It does not consider the incidence of adverse reactions and their effect on patients’ preferences. Here we include the costs of treating adverse reactionsand calculate the total benefit in terms of how much the new drug can reduce societal expenditure.We describe how our model may be used for the design of phase III clinical trials, cluster randomised clinical trials and bridging studies. This is done in some detail and using illustrative examples based on published studies. For phase III trials we allow the possibility of unequal treatment group sizes, which often occur in practice. Bridging studies are those carried out to extendthe range of applicability of an established drug, for example to new ethnic groups. Throughout the objective of our procedures is to optimise the costbenefit in terms of national health-care. BeBay is the leading methodologyfor determining sample sizes on this basis. It explicitly takes account of the roles of three decision makers, namely patients and doctors, pharmaceutical companies and the health authority.

Digital Origin:Born digital Type of Award:DPhil Level of Award:Doctoral Awarding Institution: University of Oxford Notes:Figures 1.1 and 1.2 of this thesis cannot be made available online for copyright reasons.


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 Bibliographic Details

Issue Date: 2011

Copyright Date: 2010 Identifiers

Urn: uuid:f5cb4e27-8d4c-4a80-b792-469e50efeea2 Item Description

Type: thesis;

Language: en Keywords: Bayesian cost-benefit sample sizes evalution clinical trials bridging studiesSubjects: Statistics (see also social sciences) Tiny URL: ora:5732


Author: Dr Takashi Kikuchi - institutionUniversity of Oxford facultyMathematical,Physical and Life Sciences Division - Statistics oxfordC

Source: https://ora.ox.ac.uk/objects/uuid:f5cb4e27-8d4c-4a80-b792-469e50efeea2


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