Single or multicentre trials

This section contains the following:


Single Centre
Single centre trials are usually set up in a particular hospital, clinic or general practice.  They are usually small-scale studies, cheaper to conduct than multicentre trials and therefore generally easier to obtain funding for.  Single centre trials provide the flexibility of approach necessary for clinicians and scientists to develop new treatments and can provide an important source for new therapeutic ideas.  In a single centre trial the clinical investigators are often continuously involved and maintain enthusiasm throughout.

Problems and solutions
Many single centre trials often recruit too few patients to be scientifically viable.  A trial with only a small number of participants carries a considerable risk of failing to demonstrate a treatment difference when one is really present i.e. type II error.  Often a single source of participants may be insufficient to make a clinical trial of viable size.  This problem may be clear-cut from the beginning but on other occasions it may linger on with too few participants and finally peter out as enthusiasm wanes.  Thus, it is important to recognise early on whether a single centre trial is feasible and scrutinise the ethics, organisation and relevance of it carefully.

Multicentre trials
Multicentre trials are carried out for two main reasons.  Firstly, a multicentre trial is an accepted way of evaluating a new technology more efficiently; under some circumstances, it may present the only practical means of accruing sufficient subjects to satisfy the trial objective within a reasonable time frame.  Multicentre trials of this nature may, in principle, be carried out at any stage of clinical development.  They may have several centres with a large number of subjects per centre or, in the case of a rare disease, they may have a large number of centres with very few subjects per centre.

Secondly, a trial may be designed as a multicentre (and multi-investigator) trial primarily to provide a better basis for the subsequent generalisation of its findings.  This arises from the possibility of recruiting the subjects from a wider population and of delivering the technology in a broader range of clinical settings, thus presenting an experimental situation that is more typical of future use.  The involvement of a number of investigators also gives the potential for a wider range of clinical judgements concerning the value of the technology.  Such a trial would be a confirmatory trial in the later phases of technology development and would be likely to involve a large number of investigators and centres.  It might sometimes be conducted in a number of different countries in order to facilitate generalisability even further.

Problems and solutions
Multi-centre trials are considerably more complex (e.g. co-ordination, quality control, data management) than single center trials and therefore it is essential to have efficient central co-ordination of all trial activities (see Trial co-ordination).  They are also very expensive to run both in terms of personnel and resources and therefore require adequate funding form the onset.  If a multicentre trial is to be meaningfully interpreted and extrapolated, then the manner in which the protocol is implemented should be clear and similar at all centres.  Furthermore, the usual sample size and power calculations depend upon the assumption that the differences between the compared treatments in the centres are unbiased estimates of the same quantity.  It is important to design a common protocol and to conduct the trial with this background in mind.  Procedures should be standardised as completely as possible.  Variation of evaluation criteria and schemes can be reduced by investigator meetings, by the training of personnel in advance of the trial and by careful monitoring during the trial.  Good design should generally aim to achieve the same distribution of subjects to treatments within each centre and good management should maintain this design objective.  Finally, one particular difficulty is to motivate all participants in a large multicentre trial to play an enthusiastic and responsible role.  In this respect, collaborator meetings, regular newsletters and feedback of general information on the trial’s progress may help (see Sources or methods of recruitment).

It is worth noting that the key to a successful multicentre trial is trial management (see Trial management ).  Trial managers typically require a range of skills and are crucial to the successful running of a trial.  He or she may be required to spend up to 50% of their time communicating with or traveling to the outlying centres.

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Things to consider when writing a protocol

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Additional resources

Trial Protocol Tool resource icon Multicentre trial checklist

This checklist has been modified from a checklist prepared for the International Conference on Harmonization Guideline for Good Clinical Practice (ICH GCP)

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Further reading

Blumenstein BA, James KE, Lind BK, Mitchell HE. Functions and Organization of Coordinating Centers for Multicenter Studies. Controlled Clinical Trials 1995;16: 4S-29S.

Pocock SJ. (1983) Clinical Trials: A Practical Approach. John Wiley and Sons, Chichester.

Duley L and Farrell B.  Clinical Trials. London: BMJ Books, 2002.

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This page was last updated 16th December 2003.