手法を比較

	E-I Index	ソーシャルネットワーク分析
分野	Sociology	ネットワーク分析
系統	Process / pipeline	Machine learning
提唱年	1988	1934 (sociometry); 1994 (modern formalization)
提唱者	David Krackhardt & Robert Stern	Moreno, J.L.; formalized by Wasserman & Faust
種類	Index of the relative balance of between-group versus within-group ties	Structural/relational analysis framework
原典	Krackhardt, D., & Stern, R. N. (1988). Informal networks and organizational crises: An experimental simulation. Social Psychology Quarterly, 51(2), 123–140.	Wasserman, S. & Faust, K. (1994). Social Network Analysis: Methods and Applications. Cambridge University Press. ISBN: 978-0-521-38707-1
別名	EI index, external-internal index, Krackhardt-Stern E-I ratio, E/I ratio	SNA, network analysis, sociometric analysis, relational analysis
関連	5	5
概要	The external-internal (E-I) index, introduced by Krackhardt and Stern, measures the extent to which the ties of a group point outward to other groups versus inward to its own members. It is the number of between-group (external) ties minus the number of within-group (internal) ties, divided by the total number of ties. Ranging from −1 (all ties internal, perfect insularity) to +1 (all ties external), it is a compact summary of homophily and group closure that can be computed for a whole network, for each group, or for each node.	Social Network Analysis (SNA) is a structural method that maps and measures relationships and flows between people, groups, organizations, or other entities modeled as nodes connected by ties (edges). Rather than focusing on individual attributes, SNA reveals how the pattern of connections shapes behavior, influence, information flow, and outcomes within a system.