Abstract
.In addition to the direct effect of insecticide-treated nets (ITNs), there has been evidence for spatial indirect effects. Spatial analyses in cluster randomized trials (CRTs) are rare, but a large-scale CRT from 1993 was one of the first to conduct a spatial analysis of ITNs in CRTs. We revisit these data by applying a broader range of contemporary spatial methods to further explore spatial spillover. We conducted three analyses: 1) exploratory spatial analysis, considering spatial patterns and spillover in the data; 2) spatial modeling, estimating the intervention effect considering spatial effects; and 3) analysis of distance-based spillover and interaction with the intervention, characterizing the functional distance over which the spillover effect was present. There were consistent indications of spatial patterns from the exploratory analysis. Bed nets were associated with a 17% reduction in all-cause mortality for children aged 6–59 months, and the intervention estimate remained robust when allowing for the spatial structure of the data. There was strong evidence of a spatial spillover effect: for every additional 100 m that a control household was from an intervention household (and vice versa), the standardized mortality ratio (SMR) increased by 1.7% (SMR 1.017, 95% credible interval 1.006–1.026). Despite evidence of a spatial spillover effect, the conclusions of the trial remain unaffected by spatial model specifications. Use of ITNs was clearly beneficial for individuals, and there was compelling evidence that they provide an indirect benefit to individuals living nearby. This article demonstrates the extra utility that spatial methods can provide when analyzing a CRT.
Highlights
A series of cluster randomized trials (CRTs) carried out two decades ago in endemic areas in Africa demonstrated strong evidence that insecticide-treated bed nets (ITNs) can reduce child mortality.[1,2,3,4,5] For instance, a large-scale CRT of ITNs in the Kassena-Nankana (Navrongo) district of northern Ghana found a 17% reduction in all-cause child mortality in children aged 6 months to 4 years.[3]
We examined the existence of spatial spillovers and the impact of spatial effects on the overall trial conclusions in a CRT of ITNs
Our analysis suggests that for every additional 100 m a control household was from an intervention household, the standardized child mortality ratio increased by 1.7% (SMR 1.017, 95% credible intervals (CrIs): 1.006–1.026)
Summary
A series of cluster randomized trials (CRTs) carried out two decades ago in endemic areas in Africa demonstrated strong evidence that insecticide-treated bed nets (ITNs) can reduce child mortality.[1,2,3,4,5] For instance, a large-scale CRT of ITNs in the Kassena-Nankana (Navrongo) district of northern Ghana found a 17% reduction in all-cause child mortality in children aged 6 months to 4 years (standardized mortality ratio [SMR] 0.83, 95% CI: 0.69–1.00).[3]. In addition to the direct effect, there was evidence for positive spillovers, or spatial indirect effects.[6,7,8] Using data from the Navrongo CRT, a subsequent study by Binka et al.[9] found reductions in mortality among individuals without ITNs who lived close to individuals who did. From a recent systematic review, this example of positive spillover was found to be the first evidence of a spatial indirect effect of the bed net intervention, in addition to the direct effect that ITNs had in reducing mortality for those using them.[10] Binka et al used information on household location to gain insight into spatial indirect effects. Subsequent analyses have demonstrated positive spillover with ITNs,[5,7,8,11,12] at least one study failed to find evidence of spatial indirect effects.[13]
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