There are regional differences in the English language, and Cochrane Review Groups support both British (i.e. UK) and American (i.e. US) English. Cochrane Reviews should use one type of English throughout.
The ‘-ize’ suffix (e.g. randomize) is often associated with US English and ‘-ise’ (e.g. randomise) with British English, when in fact ‘-ize’ is also commonly used in British English. Cochrane Reviews can use either spelling but the choice should be applied consistently within a single Cochrane Review or document.
Note that the Cochrane brand guidelines state a preference for UK English with '-ize' spelling.