Are `Water Smart Landscapes' Contagious? An epidemic approach on networks to study peer effects

TL;DR

This study investigates whether participation in the Water Smart Landscapes program in Las Vegas spreads among households through neighborhood peer effects, using epidemic models to analyze 15 years of geo-coded data.

Contribution

It introduces epidemic spreading models, specifically SEIR, to detect peer effects in environmental program participation, offering a flexible alternative to hazard models.

Findings

Evidence of peer effects in multiple neighborhoods

Epidemic models effectively capture contagion in participation

Supports the use of epidemic models for social influence analysis

Abstract

We test the existence of a neighborhood based peer effect around participation in an incentive based conservation program called `Water Smart Landscapes' (WSL) in the city of Las Vegas, Nevada. We use 15 years of geo-coded daily records of WSL program applications and approvals compiled by the Southern Nevada Water Authority and Clark County Tax Assessors rolls for home characteristics. We use this data to test whether a spatially mediated peer effect can be observed in WSL participation likelihood at the household level. We show that epidemic spreading models provide more flexibility in modeling assumptions, and also provide one mechanism for addressing problems associated with correlated unobservables than hazards models which can also be applied to address the same questions. We build networks of neighborhood based peers for 16 randomly selected neighborhoods in Las Vegas and test for the existence of a peer based influence on WSL participation by using a Susceptible-Exposed-Infected-Recovered epidemic spreading model (SEIR), in which a home can become infected via autoinfection or through contagion from its infected neighbors. We show that this type of epidemic model can be directly recast to an additive-multiplicative hazard model, but not to purely multiplicative one. Using both inference and prediction approaches we find evidence of peer effects in several Las Vegas neighborhoods.