In recent years, ecologists and epidemiologists have paid increasing
attention to the influence of spatial structure in shaping the dynamics
and determining the persistence of populations. This is fundamentally affected
by the concept of ``coupling'' -- the flux of individuals moving between
separate populations. In this paper, we contrast how coupling is typically
implemented in epidemic models with more detailed approaches. Our aim is
to link the popular phenomenological formulations with the results of mechanistic
models. By concentrating on the behaviour of simple epidemic systems, we
relate explicit movement patterns with observed levels of coupling, validating
the standard formulation. The analysis is then extended to include a brief
study of how the correlation between stochastic populations is affected
by coupling, the underlying deterministic dynamics and the relative population
sizes.