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Fig. 1 | BMC Medicine

Fig. 1

From: Simulations for designing and interpreting intervention trials in infectious diseases

Fig. 1

Study designs for dependent happenings. Two clusters, or populations, are considered under two different scenarios. In the left-hand side scenario, a certain portion of individuals in the cluster receive vaccination (or other treatment) (Z = 1) and the remaining portion receive the control intervention (Z = 0). In the right-hand side scenario, everyone receives the control intervention. Control is defined as current best practice, placebo, or nothing. The direct, indirect, total, and overall effects of intervention are defined by the indicated contrasts (adapted from Halloran and Struchiner [2, 3]). The effects have recently been given alternative terms in the economics literature [4], where ‘direct effect’ is termed as ‘value of treatment’, ‘indirect effect’ as ‘spillover effect on the non-treated’, ‘overall effect’ as ‘total causal effect’, and ‘total effect’ as ‘intention-to-treat effect’

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