Social network targeting to maximise population behaviour change: a cluster randomised controlled trial
Summary
Background
Information
and behaviour can spread through interpersonal ties. By targeting
influential individuals, health interventions that harness the
distributive properties of social networks could be made more effective
and efficient than those that do not. Our aim was to assess which
targeting methods produce the greatest cascades or spillover effects and
hence maximise population-level behaviour change.
Methods
In
this cluster randomised trial, participants were recruited from
villages of the Department of Lempira, Honduras. We blocked villages on
the basis of network size, socioeconomic status, and baseline rates of
water purification, for delivery of two public health interventions:
chlorine for water purification and multivitamins for micronutrient
deficiencies. We then randomised villages, separately for each
intervention, to one of three targeting methods, introducing the
interventions to 5% samples composed of either: randomly selected
villagers (n=9 villages for each intervention); villagers with the most
social ties (n=9); or nominated friends of random villagers (n=9; the
last strategy exploiting the so-called friendship paradox of social
networks). Participants and data collectors were not aware of the
targeting methods. Primary endpoints were the proportions of available
products redeemed by the entire population under each targeting method.
This trial is registered with
ClinicalTrials.gov, number
NCT01672580.
Findings
Between
Aug 4, and Aug 14, 2012, 32 villages in rural Honduras (25–541
participants each; total study population of 5773) received public
health interventions. For each intervention, nine villages (each with
1–20 initial target individuals) were randomised, using a blocked
design, to each of the three targeting methods. In nomination-targeted
villages, 951 (74·3%) of 1280 available multivitamin tickets were
redeemed compared with 940 (66·2%) of 1420 in randomly targeted villages
and 744 (61·0%) of 1220 in indegree-targeted villages. All pairwise
differences in redemption rates were significant (p<0·01) after
correction for multiple comparisons. Targeting nominated friends
increased adoption of the nutritional intervention by 12·2% compared
with random targeting (95% CI 6·9–17·9). Targeting the most highly
connected individuals, by contrast, produced no greater adoption of
either intervention, compared with random targeting.
Interpretation
Introduction
of a health intervention to the nominated friends of random individuals
can enhance that intervention's diffusion by exploiting intrinsic
properties of human social networks. This method has the additional
advantage of scalability because it can be implemented without mapping
the network. Deployment of certain types of health interventions via
network targeting, without increasing the number of individuals targeted
or the resources used, could enhance the adoption and efficiency of
those interventions, thereby improving population health.
Funding
National
Institutes of Health, The Bill & Melinda Gates Foundation, Star
Family Foundation, and the Canadian Institutes of Health Research.
Article Info