Table 1 Examples of adequate and inadequate allocation concealment

Centralized randomization procedures in which the persons including a patient contact the randomization center or a person otherwise not involved in the trial who registers the patient as included in the trial and only then provides the allocation information for this patient

An open random allocation schedule, that is, where all future allocations can be read by an investigator

Any computerized system that ensures, by password protection or other computer security procedures, conditions 1 and 2 described in the text

Envelopes, if clear details of the procedures used to avoid allocation becoming unconcealed are inadequate, or unclear

Use of consecutively numbered, opaque sealed envelopes containing the allocation information kept by a person otherwise not involved in the study with envelopes opened only after registration of an included patient

Assignment envelopes were used without appropriate safeguards (for example if envelopes were unsealed or non-opaque or not sequentially numbered)

Alternation, rotation, day of the week

Date of birth, or medical record number

Blocked randomization with block size known to the person including the patient

An unspecified method, for example, if the report states only that "patients were randomized" without giving details of the exact procedures used, and no further information is obtained from the authors.