Krackhardt E/I Ratio
The Krackhardt E/I Ratio (or variously the E-I Index) is a social network measure which the relative density of internal connections within a social group compared to the number of connections that group has to the external world. It was so described in a 1988 paper by David Krackhardt and Robert N. Stern noting the increased effectiveness in moments of crisis of organizations which had stronger informal networks that crossed formal internal group structures.
It is defined by Krackhardt and Stern in their 1985 article as follows: E-I Index = (EL-IL)/(EL+IL), where EL represents the number of edges that are external to a given subgroup and IL is the number of edges internal to or between vertexes within that subgroup.
In order to compare E-I index across networks, the final value may be normalized by dividing the E-I index by the total number of possible external ties (Mariolis 1985).
Comparisons with network theory
The E/I ratio is related to the concept of conductance, which measures the likelihood that a random walk on a subgraph will exit that subgraph.
References
- Informal networks and organizational crises: An experimental simulation. David Krackhardt, Robert N. Stern - Social Psychology Quarterly, 1988