Burt's constraint is higher if ego has less, or mutually
stronger related (i.e. more redundant) contacts. Burt's measure of
constraint, \(C_i\), of vertex \(i\)'s ego network
\(V_i\), is defined for directed and valued graphs,
$$C_i=\sum_{j \in V_i \setminus \{i\}} (p_{ij}+\sum_{q \in V_i
\setminus \{i,j\}} p_{iq} p_{qj})^2$$
for a graph of order (ie. number of vertices) \(N\), where
proportional tie strengths are defined as
$$p_{ij} = \frac{a_{ij}+a_{ji}}{\sum_{k \in V_i \setminus \{i\}}(a_{ik}+a_{ki})},$$
\(a_{ij}\) are elements of \(A\) and the latter being the
graph adjacency matrix. For isolated vertices, constraint is undefined.