9.3.7  Multiple body parts I: body parts receive the same intervention

In some studies, people are randomized, but multiple parts (or sites) of the body receive the same intervention, a separate outcome judgement being made for each body part, and the number of body parts is used as the denominator in the analysis. For example, eyes may be mistakenly used as the denominator without adjustment for the non-independence between eyes. This is similar to the situation in cluster-randomized trials, except that participants are the ‘clusters’. See methods described in Chapter 16 (Section 16.3).