Table 2.

Calculation details for the growth PA and the TC effects

Model	Formula	Description
Preferential attachment (PA)	$PA\left(i\right)={\displaystyle \sum }_j{x}_{ij}{\displaystyle \sum }_h{x}_{hj}$	Analyses the popularity of each individual. This effect reflects individual preference for links with popular individuals (i.e., individuals with the highest degrees receive more incoming links). PA(i) is defined, for individual i, as the number of relations received by individual j, to whom i is linked. Here xij in {0, 1} denotes a link between i and j.
Triadic closure (TC)	$TC\left(i\right)={\displaystyle \sum }_{j,h}{x}_{ij}{x}_{ih}{x}_{jh}$	Analyses the transitivity of the connection pattern for each individual. This describes the « friends of my friends are my friends » phenomenon. TC(i) is the number of transitive patterns including individual i in the network, that is, i is linked to j and h, which are also linked together. Here xij in {0, 1} denotes a link between i and j.