An Example of Spillover

A community policing program implemented in some neighborhoods may inadvertently affect the crime rate in some other adjacent neighborhoods.

Scientific Interest in Spillover

• Epidemiology: curtailment of infectious disease
• Sociology: peer influence through social network
• Political science: Individual electoral participation due to social pressure
• Business: innovation diffusion between firms

Spillover as a Question of Moderation

For example, vaccination on an individual would have a strong effect if many others are not vaccinated and a weak effect if many others are vaccinated.

Spillover as a Question of Mediation

For example, banning smoking in office buildings may benefit individual health through changing not only one’s own smoking behavior (first mediator) but also the smoking behavior of one’s office-mates (second mediator).