This is an archived version of the Handbook. For the current version, please go to or search for this chapter here.  Methods of sequence generation with unclear risk of bias

A simple statement such as ‘we randomly allocated’ or ‘using a randomized design’ is often insufficient to be confident that the allocation sequence was genuinely randomized. It is not uncommon for authors to use the term ‘randomized’ even when it is not justified: many trials with declared systematic allocation are described by the authors as randomized. If there is doubt, then the adequacy of sequence generation should be considered to be unclear.


Sometimes trial authors provide some information, but they incompletely define their approach and do not confirm some random component in the process. For example, authors may state that blocked randomization was used, but the process of selecting the blocks, such as a random number table or a computer random number generator, was not specified. The adequacy of sequence generation should then be classified as unclear.