Build Bipartite Affiliation Networks
Keep actors and events as separate node sets so shared participation remains observable before any one-mode projection.
Method sources
By the end of this tutorial
- 1Define bipartite or two-mode network structure from an explicit node, tie, boundary, direction, weight, and observation-window specification.
- 2Apply and audit this procedure: Construct a rectangular student-by-activity incidence matrix, verify row and column totals, calculate degree for both modes, inspect connected components, and visualize the two node types with distinct shapes.
- 3Interpret the result with a sensitivity check and the following evidence boundary: Shared activity membership creates opportunity for contact but does not demonstrate friendship, collaboration, equal participation, or influence.
SNA
Network specification
Analysis scenario
A university wants to understand how students encounter one another through clubs, research teams, and service projects during one academic year.
Nodes
Two disjoint sets: all consenting students and all eligible co-curricular activities offered during the year.
Ties
A student-to-activity membership link supported by the official participation record for the same academic year.
Network type
Undirected, binary bipartite affiliation network with no student-student or activity-activity edges and explicit zero-participation students.
Step-by-step tutorial
Freeze the relational question
Write the decision the analysis must inform, then lock the eligible node roster, tie-generating event, direction, weight, self-tie rule, observation window, and missing-data code. Preserve a read-only source copy and record why this specification represents the stated question.
Checkpoint
A second analyst can reconstruct the same node set and edge table from the written rules without guessing what an absent record means.
Compute the focal structure
Work on a versioned analysis copy and carry out the focal method exactly as specified: Construct a rectangular student-by-activity incidence matrix, verify row and column totals, calculate degree for both modes, inspect connected components, and visualize the two node types with distinct shapes. Save software and package versions, every threshold, normalization, seed, and intermediate count needed to reproduce the result.
Checkpoint
The output is tied to one named data version and includes the denominator, parameter settings, and a reproducible calculation record.
Run a structural sensitivity check
Repeat the analysis under at least one defensible alternative boundary, missingness rule, tie threshold, weight transformation, or model setting. Compare membership and substantive conclusions, not only a single coefficient, and investigate every change large enough to alter a decision.
Checkpoint
The audit states which patterns persist, which actors or groups change classification, and which conclusion depends on an analyst choice.
Report for responsible action
Pair the numerical result with a table or structure-preserving visual, document excluded and missing actors, and explain uncertainty in plain language. Convert the finding into a reversible support question, not an automatic ranking, while stating this boundary: Shared activity membership creates opportunity for contact but does not demonstrate friendship, collaboration, equal participation, or influence.
Checkpoint
The final note contains the question, specification, result, sensitivity evidence, uncertainty, privacy controls, and a proportionate next step.
Interpret with care
bipartite or two-mode network structure describes a property of the specified relation and network boundary. It does not transfer automatically to another relation, time period, class, platform, or population.
Shared activity membership creates opportunity for contact but does not demonstrate friendship, collaboration, equal participation, or influence. Compare the result with raw counts, missingness, plausible alternative specifications, and contextual evidence before acting.