Parameter distribution plots of the four significant correlations and the corresponding linear fitting results. (a) Intrinsic X-ray luminosity vs. black hole mass. (b) Intrinsic X-ray luminosity vs. Eddington ratio. (c) Eddington ratio vs. power-law spectral index. (d) Soft X-ray variability amplitude vs. hard X-ray variability amplitude. The red line is the best linear fit. The linear relation is shown in the upper-left corner of each plane, together with the Pearson correlation coefficient (R) and chance probability (P).