A ‘split body trial’ refers to when randomization of interventions takes place within individuals, with different interventions being applied to different body parts (e.g. to the two eyes or to teeth in the two sides of the mouth).

In November 2019, the Cochrane Musculoskeletal, Oral, Skin and Sensory Review Group Network Network held a web-clinic in which Tanya Walsh and Helen Worthington discussed methodological advantages and disadvantages with using data from split-body trials in Cochrane Reviews. 

As a result of this meeting, this guidance document was produced. It is not intended to act as a detailed statistical guide, rather it provides high level guiding questions to help editors identify whether this data has been used appropriately. 

You can access the full guidance here.