A trial in which each of the groups involved will receive each of the treatments, but in a randomized order: that is, they will start in one arm of the trial, but will deliberately ‘cross over’ to the other arm(s) in turn.
An appreciation of the need to account for chance and bias has led to development of methods where new treatments are compared to either a PLACEBO or to the standard treatment (or both) in a controlled, randomised clinical trial. ‘Controlled’ means that there is a comparison group of patients not receiving the test intervention, and ‘randomised’ implies that patients have been assigned to one or other treatment group entirely by chance and not because of their doctor’s preference. If possible, trials are ‘double-blind’ – that is, neither the patient nor the investigator knows who is receiving which intervention until after the trial is over. All such trials must follow proper ethical standards with the procedure fully explained to patients and their consent obtained.
The conduct, e?ectiveness and duplication of clinical trials have long been subjects of debate. Apart from occasional discoveries of deliberately fraudulent research (see RESEARCH FRAUD AND MISCONDUCT), the structure of some trials are unsatisfactory, statistical analyses are sometimes disputed and major problems have been the – usually unwitting – duplication of trials and non-publication of some trials, restricting access to their ?ndings. Duplication occurs because no formal international mechanism exists to enable research workers to discover whether a clinical trial they are planning is already underway elsewhere or has been completed but never published, perhaps because the results were negative, or no journal was willing to publish it, or the authors or funding authorities decided not to submit it for publication.
In the mid 1980s a proposal was made for an international register of clinical trials. In 1991 the NHS launched a research and development initiative and, liaising with the COCHRANE COLLABORATION, set out to collect systematically data from published randomised clinical trials. In 1994 the NHS set up a Centre for Reviews and Dissemination which, among other responsibilities, maintains a database of research reviews to provide NHS sta? with relevant information.
These e?orts are hampered by availability of information about trials in progress and unpublished completed trials. With a view to improving accessibility of relevant information, the publishers of Current Science, in 1998, launched an online metaregister of ongoing randomised controlled trials.
Subsequently, in October 1999, the editors of the British Medical Journal and the Lancet argued that the case for an international register of all clinical trials prior to their launch was unanswerable. ‘The public’, they said, ‘has the right to know what research is being funded. Researchers and research funders don’t want to waste resources repeating trials already underway.’ Given the widening recognition of the importance to patients and doctors of the practice of EVIDENCE-BASED MEDICINE, the easy availability of information on planned, ongoing and completed clinical trials is vital. The register was ?nally set up in 2005.... clinical trials
This random allocation means individuals are equally likely to be selected for the particular treatment being investigated or for the control group of the trial.... randomized controlled trials
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