Table 1. Behavioral principles underlying the formation of patient sharing relations and their relation with predicted event sequences.

Behavioral Principle	Network effect s(i, j, t)	Relational protocols (patient sharing routine)	Predicted event sequence
			(t)	(t+Δt)
Mutuality	Reciprocity	“Share patients preferentially with partners willing to share their patients with you”	i ← j	i → j
Specialization	Assortativity	“If I need to send many patients, I send them preferentially to hospitals receiving many patients	j ← k	j ← l
Stabilization (Recency)	Repetition	“Share patients preferentially with partners with whom you have shared patients in the past”	i → j	i → j
Transitivity	Transitive Closure (“embeddedness”)	“Partners of my partners are my partners”	i → k → j	i → j
Generalized exchange	Cyclic closure	“Accept patients from partners of partners even without reciprocity”	i → k → j	i ← k ← j
			i ← j	i → j