John Gittins

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Sample size computations are largely based on frequentist or classical methods. In the Bayesian approach the prior information on the unknown parameters is taken into account. In this work we consider a fully Bayesian approach to the sample size determination problem which was introduced by Grundy et al. and developed by Lindley. This approach treats the(More)
In this paper we introduce a fully Bayesian approach to sample size determination in clinical trials. In contrast to the usual Bayesian decision theoretic methodology, which assumes a single decision maker, our approach recognises the existence of three decision makers, namely: the pharmaceutical company conducting the trial, which decides on its size; the(More)
The beam and performance characteristics of a new orthovoltage X-ray unit, the Pantak DXT-300 have been evaluated. Data were collated for four qualities: 3.27 mmAl, 7.15 mmAl, 1.65 mmCu and 3.51 mmCu half value layer (HVL) (SE = 0.04 mm). Parameters which were investigated included beam quality, central axis depth dose, relative output, backscatter factors,(More)
Transcranial Doppler ultrasound (TCD) is commonly used to detect embolic signals in the cerebral circulation. However, current techniques to discriminate between signals from emboli and artifacts are subjective and ambiguous. The radiofrequency (RF) signal provides an extra dimension to the information available from conventional TCD systems that may help(More)
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 the 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(More)
The potential benefits of washing eggs is offset by a historical perception in the European Union that wetted eggs are prone to spoilage and water loss. This study describes the effects of spray jet washing under various processing conditions to shell surface counts of Salmonella and the presence of bacteria in egg contents. Experiments used eggs that were(More)
It is necessary for the calculation of sample size to achieve the best balance between the cost of a clinical trial and the possible benefits from a new treatment. Gittins and Pezeshk developed an innovative (behavioral Bayes) approach, which assumes that the number of users is an increasing function of the difference in performance between the new(More)
The behavioural Bayes approach to sample size determination for clinical trials assumes that the number of subsequent patients switching to a new drug from the current drug depends on the strength of the evidence for efficacy and safety that was observed in the clinical trials. The optimal sample size is the one which maximises the expected net benefit of(More)
PURPOSE To establish whether it is possible to improve orbicularis oculi muscle function in the eyelids of patients with a chronic seventh cranial nerve palsy by using transcutaneous electrical stimulation to the point at which electrical stimulation induces a functional blink. METHODS Ten subjects (one woman, nine men) aged 36 to 76 with chronic,(More)
Doppler flow and string phantoms have been used to assess the performance of ultrasound Doppler systems in terms of parameters such as sensitivity, velocity accuracy and sample volume registration. However, because of the nature of their construction, they cannot challenge the accuracy and repeatability of modern digital ultrasound systems or give objective(More)