The International Standard Randomised Controlled Trial Number (ISRCTN): what does it mean for reviewers?

Objectives

For researchers conducting systematic reviews, difficulties can arise in determining publications that refer to the same trial, for example where authors differ, or where numbers included in analyses vary between publications. Similar difficulties occur where a trial is included in more than one register, for example where titles differ between registers. Such problems could lead to double counting and potentially, inclusion of a trial more than once in a systematic review and consequently receiving undue weight in any quantitative analyses. Therefore an internationally accepted, uniform system of unique trial identifiers would be extremely useful to reviewers, making it immediately apparent where multiple reports or register entries refer to an individual trial. During the last year, considerable progress has been made in establishing such a system. Although in its infancy, the ISRCTN scheme has been launched. Once fully operational, it should increase prospective registration of RCTs internationally. We aim to highlight the benefits of this system to systematic reviewers.

Methods

The combined efforts of a number of groups interested in the issues of trial registration have lead to the implementation of ISRCTNs. Although the concepts underpinning the scheme are not new, it represents the first time unique identifiers have been assigned to RCTs on an international basis. The scheme, overseen by an independent advisory group, is managed by Current Controlled Trials, who are also responsible for the metaRegister of Controlled Trials (mRCT).

Results

In order to test the system, a series of randomly generated, 8-digit numbers from a central source were allocated to the British Medical Research Council (MRC) clinical trials group, and assigned to ongoing RCTs in cancer. These ISRCTNs were recorded within the MRC trials directory and the UKCCCR register of cancer trials, both of which contribute information to the mRCT, the central resource for the ISRCTN scheme. Following extensive testing, assigning of ISRCTNs was expanded to include all MRC-funded RCTs, and trials funded by the UK Cancer Research Campaign (administered by the UKCCCR Register). Funding organisations and individual trialists will be invited to participate in the scheme, such that future developments include all RCTs.

Conclusions

The initiation of this system should benefit reviewers in a number of ways. Firstly, it should in future promote widespread prospective registration, the advantages of which are widely accepted by meta-analysts and systematic reviewers, and provide a more complete public record of RCTs, through the mRCT and contributing registers. The numbering system should facilitate identification of trials that appear on more than one register, and so help to prevent "double-counting" of trials. Furthermore, as the scheme progresses, it is envisaged that journal editors will require ISRCTNs for all trials submitted for publication. This should further facilitate trial searching and allow reviewers to more easily identify duplicate publications of individual trials.

This abstract has been presented by the authors on behalf of the ISRCTN Working Group

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