Longitudinal analysis of friendship networks

This note discusses and demonstrates methods, both exploratory and confirmatory, for analysing data from friendship networks collected over time. The focus is on stochastic models for dyadic interaction designed to quantify the structural effect of reciprocity on arc changes. The networks studied were previously analysed by Hallinan (Social Networks 1: 193-210) who was concerned with stability of dyadic choices and the direction of change of asymmetric dyads to either mutual or null dyads. These aspects of the networks are really of secondary importance to the effect of reciprocated choices on the probabilities of dyadic change. Measures of this 'reciprocity effect' are presented, and comments on the rationale for continuous-time Markov chains as models for networks are given.