2000115-Strengthening-Communities-with-Neighborhood-Data

374 Strengthening Communities with Neighborhood Data
residents in both tracts, shared economic conditions in both tracts (such
as a factory closing that affected both or cheaper land values in both),
and interactions between these dynamics. In spatial point pattern analysis,
the difference between “true and apparent contagion” (with origins
in epidemiology) is analogous to that between spatial dependence and
spatial heterogeneity in the analysis of spatial areas. In a process of true
contagion, two people end up with a similar characteristic as a result of
an interaction in which the characteristic was transmitted or shared. In
a process of apparent contagion, two people have similar characteristics,
but this similarity is independent of any interaction they might have.
True and apparent contagions are observationally equivalent (i.e., the
same observed results could be reached through different unobserved
processes). Since the underlying spatial process that drives the observed
spatial pattern is unobserved, true and apparent contagion cannot be
distinguished in a cross-sectional context without additional information,
such as additional spatially independent observations or additional
observations from different time periods.
Spatial feedback effects that exist under conditions of true contagion
violate the lack of interaction assumption whereby treatments for one
person do not influence others’ outcomes. This logic of independence
was based on randomized controlled trials designed to isolate impacts
of single interventions. However, part of what makes spatially clustered
problems “wickedly complex” is that they have interacting causes (Bellefontaine
and Wisener 2011). Here individual-level outcomes are often
dependent, as in spillover effects on a single outcome or between different
outcomes (Bloom 2005). In spillovers among single outcomes,
the outcome of one or more people influences that of others (e.g., in
peer effects, when employment increases as a result of networking with
employed neighbors). Spillovers between different outcomes occur when
one outcome influences a different one, as in neighborhood effects when
the chance that a child does well in school would be lower in a neighborhood
of concentrated poverty than in a more affluent one.
At the aggregate level, the concept of spatial dependence can focus
attention on potential interactions between a target area and neighboring
areas, including intended and unintended consequences. For instance,
one such question is whether a place-based approach has positive spatial
externalities (such as economic multiplier effects in neighboring areas)
or negative spatial externalities (which may occur if a crime reduction
effort in one precinct ends up displacing crime to nearby precincts, 1 or if