Randomised clinical trials

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The randomised clinical trial is widely accepted as the gold standard, and the most rigorous way of evaluating treatments. Its principal strength lies in minimisation of bias, which allows clinically important effects due to interventions to be identified. This in turn helps to generate high-quality data, which can potentially inform effective treatment strategies. Terminology The term ‘clinical trial’ is often used loosely to describe a variety of study designs. Non- randomised trials represent studies where outcomes in patients subjected to the ʼnew’ treatment are compared with those in a set of historical or concurrent controls, in what is essentially a cohort design. While the use of historical retrospective controls can bias the results in favour of a new treatment, partly owing to a more rigorous system of patient selection and partly owing to better systems of data collection for the new treatment, comparison of trials of the same treatment with randomised or historic controls has been shown to yield more optimistic results with historic controls. Use of concurrent controls may also lead to erroneous results due to problems with self-selection of patients into the experimental and control groups. The strength of randomised clinical trials lies in the fact that allocation of treatment is based on chance rather than intention; random allocation ensures that there should be no systematic differences between the groups in known or unknown factors that could affect any of the outcomes. Randomised clinical trials may be classified in a number of ways (see Table 10.1). Some of these are discussed below. Pilot Studies A pilot or feasibility study, whenever possible, is a crucial initial step in a good study design, increasing the likelihood of success with the main study. The purpose of a pilot study includes evaluating the feasibility of recruitment, randomisation, retention of the participants and appropriate implementation of the intervention that is being tested, and assessment of the value of tools used to measure outcomes, such as quality of life questionnaires.

Original languageEnglish
Title of host publicationIntroduction to Research Methodology for Specialists and Trainees
EditorsP.M. Shaughn O'Brien, Fiona Broughton-Pipkin
PublisherCambridge University Press
Number of pages12
ISBN (Electronic)9781107585775
ISBN (Print)9781107699472
Publication statusPublished - 1 Jan 2017


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