To maintain the integrity of randomization, it is always advisable to ensure a degree of separation between those responsible for entering patients into trials, and those responsible for setting up the randomization schedule. This is best achieved when randomization can be performed by contacting a central office, either by telephone or through remote access to a computer-based randomization system. As a minimum, when pre-prepared randomization lists are to be used in a trial, they should be prepared and kept by someone not involved in treating trial patients. For local studies, a computer-based system may provide an extra level of security, though issues concerning maintaining the integrity of randomization - such as concealing the block size used - still apply when setting these up. The system should therefore not be set up by the person who will be responsible for inviting patients to take part in the trial.
Whenever a computer-based system is used, a back-up system is useful in case of computer failure. Ideally this should comprise pre-prepared randomization lists, but for very occasional emergency use, it is possible simply to throw a dice or toss a coin. The patient's details and allocated treatment should always be recorded and added to the main system as soon as possible.
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