Relation between the fractal dimension and the cluster age in Pang catalog clusters (left panels) and in Hunt catalog clusters (right panels) in the solar neighborhood for the all-member region (a and d), r > r_t (b and e), and r ≤ r_t (c and f). The colored open symbols and curves in panels a and d represent the evolution of the fractal dimension taken from the simulations by Ussipov et al. (2024) with SFEs of 0.15 (purple circles), 0.17 (red triangles), and 0.20 (orange crosses). The quantity s is Spearman’s rank correlation coefficient, and p is the probability of the null hypothesis in the correlation test. A p-value less than 0.05 means rejection of the null hypothesis.