Relations between the fraction of 2P AGB stars (f_2P,AGB) and the selected GC global parameters. The data points were all derived using the criteria defined in Sect. 5.1. Filled and open circles are used, respectively, for the five GCs we analyzed self-consistently (NGC 6809, NGC 2808, NGC 6121, NGC 104, and NGC 6752) and for those we took from the literature (NGC 6205, NGC 5986, NGC 5904, and NGC 6266). The associated error bars are computed from Beta distribution. The lines are the linear fits derived by least square fitting (with the errors taken into account); the solid and dashed lines are fitted from our own five GCs and all the nine GCs, respectively, while the dash-dotted ones represent the fits disregarding the two most scattered points of NGC 6266 and NGC 6752. The Pearson correlation coefficients considering the five (R5), nine (R9), and seven (R7) data points, respectively, are listed at the bottom of each panel (except for the very bottom right panel, which reports the five (R5), eight (R8), and six (R6) data points, as no σ_v data is available for NGC 5986).