The outbreak of epidemics, the rise of religious radicalization
or the motivational influence of fellow students in classrooms
are some of the issues that can be described as diffusion
processes in heterogeneous groups. Understanding the role
that interaction patterns between groups (e.g. homophily or
segregation) play in the diffusion of certain traits or behaviours
is a major challenge for contemporary societies. Here, we study
the impact on diffusion processes of mixing (or, alternatively,
segregating) two groups that present different sensitivities or
propensities to contagion. We find non-monotonic effects of
mixing and inefficient segregation levels, i.e. situations where
a change in the mixing level can benefit both groups, e.g.
where an increase in the mixing level can reduce the expected
contagion levels in both groups. These findings can have
fundamental consequences for the design of inclusion policies.
