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9.3.9  Multiple intervention groups

Studies that compare more than two intervention groups need to be treated with care. Such studies are often included in meta-analysis by making multiple pair-wise comparisons between all possible pairs of intervention groups. A serious unit-of-analysis problem arises if the same group of participants is included twice in the same meta-analysis (for example, if ‘Dose 1 vs Placebo’ and ‘Dose 2 vs Placebo’ are both included in the same meta-analysis, with the same placebo patients in both comparisons). See Chapter 16 (Section 16.5).