Traditionally the passive voice has been used by scientists and medical professionals on the basis that what happened was considered to be more important than who did it. However, use of the passive has declined, and Cochrane reviews should use the active voice where possible, as it is generally more accessible and a clearer way of defining responsibilities and relationships.

Most sentences need to be written in the active voice. In situations where the identity of the subject is not important, and where the focus of the message is paramount, it is appropriate to use a passive construction. For example: 'The vitreous, retina and other internal structures in the eye can be viewed through a specialized microscope.’