We identified three primary mechanisms of spillovers : reduced disease transmission , social proximity and substitution of re sources within households .
We found the strongest evidence for spillovers through reduced disease transmission , particularly vaccines and mass drug administration .
In general , the proportion of a population receiving an intervention was associated with improved health .
We found evidence of publication bias for certain spillover estimates but not for total or direct effects .
Conclusions We found the strongest evidence for spillovers from vaccines and mass drug administration to control infectious disease .
There was little high quality evidence of spillovers for other interventions
Background Many interventions delivered to improve health may benefit not only direct recipients but also people in close physical or social proximity .
Our objective was to review all published literature about the spillover effects of interventions on health outcomes in low-middle income countries and to identify methods used in estimating these effects .
Toward Causal Inference With Interference
A fundamental assumption usually made in causal inference is that of no interference between individuals ( or units ) ; that is , the potential outcomes of one individual are assumed to be unaffected by the treatment assignment of other individuals . However , in many setting s , this assumption obviously does not hold . For example , in the dependent happenings of infectious diseases , whether one person becomes infected depends on who else in the population is vaccinated . In this article , we consider a population of groups of individuals where interference is possible between individuals within the same group . We propose estim and s for direct , indirect , total , and overall causal effects of treatment strategies in this setting . Relations among the estim and s are established ; for example , the total causal effect is shown to equal the sum of direct and indirect causal effects . Using an experimental design with a two-stage r and omization procedure ( first at the group level , then at the individual level within groups ) , unbiased estimators of the proposed estim and s are presented . Variances of the estimators are also developed . The methodology is illustrated in two different setting s where interference is likely : assessing causal effects of housing vouchers and of vaccines
We identified three primary mechanisms of spillovers : reduced disease transmission , social proximity and substitution of re sources within households .
We found the strongest evidence for spillovers through reduced disease transmission , particularly vaccines and mass drug administration .
In general , the proportion of a population receiving an intervention was associated with improved health .
We found evidence of publication bias for certain spillover estimates but not for total or direct effects .
Conclusions We found the strongest evidence for spillovers from vaccines and mass drug administration to control infectious disease .
There was little high quality evidence of spillovers for other interventions
Background Many interventions delivered to improve health may benefit not only direct recipients but also people in close physical or social proximity .
Our objective was to review all published literature about the spillover effects of interventions on health outcomes in low-middle income countries and to identify methods used in estimating these effects .