  A new understanding of the consequences of how ecosystem elements are
interconnected is emerging from the development and application of Ecological
Network Analysis. The relative importance of indirect effects is central to
this understanding, and the ratio of indirect flow to direct flow (I/D) is one
indicator of their importance. Two methods have been proposed for calculating
this indicator. The unit approach shows what would happen if each system member
had a unit input or output, while the realized technique determines the ratio
using the observed system inputs or outputs. When using the unit method, the
input oriented and output oriented ratios can be different, potentially leading
to conflicting results. However, we show that the input and output oriented I/D
ratios are identical using the realized method when the system is at steady
state. This work is a step in the maturation of Ecological Network Analysis
that will let it be more readily testable empirically and ultimately more
useful for environmental assessment and management.
