Before revision:  Here, we propose the concept of a significant tie to statistically evaluate the strength of a relationship . Application of the proposed method to the Italian interbank networks reveals that the percentage of relationship lending among all bilateral trades is consistently around 20\%-30\% and that their trading properties are distinct from those of transactional trades .
After revision:  Here, we propose the concept of a significant tie to statistically evaluate the strength of a relationship . Application of the proposed method to the Italian interbank networks reveals that the fraction of relationship lending among all bilateral trades is consistently around 20\%-30\% and that their trading properties are distinct from those of transactional trades .