Fig. 8

Correlation between the year of publication of the first volume, y, and indices of network structure. For the partial correlation coefficient, we partial out the influence of the number of nodes. According to a standard, the effect size is said to be large, moderate, or small when the correlation coefficient is \(> 0.5\), \(> 0.3\), or \(> 0.1\), respectively (Cohen 1988). The horizontal lines indicate 95% confidence intervals. N: number of nodes, \(\langle k \rangle\): average degree, \(k_{\mathrm{CV}}\): CV of the degree, \(k_{\mathrm{p}}/(N-1)\): normalized degree of the protagonist, \(\langle s \rangle\): average strength, \(s_{\mathrm{CV}}\): CV of strength, \(s_{\mathrm{p}}\): strength of the protagonist, r: degree assortativity coefficient, C: clustering coefficient, and O: temporal correlation coefficient