The Absence of the Fundamental Plane of Black Hole Activity
  An analysis of the radio and X-ray luminosities, along with black hole masses has led to a relationship, the fundamental plane of black hole activity, where logL_R = 0.60logL_X + 0.78logM_BH. We show that this same relationship can be obtained by using upper limit data or by randomizing the radio fluxes. In those cases, the relationship arises because one is effectively plotting distance vs distance in a flux-limited sample of objects. To correctly establish a relationship between L_R, L_X, and M_BH, one would need to analyze a volume-limited sample of objects. The distance effect can be removed from the sample, where a relationship between L_R/L_X and M_BH is found, showing that the L_R rises more quickly than L_X with increasing M_BH. However, until a well-define sample is used, it is unclear the degree to which this relationship is influenced by the sample-selection. 
Joel N. Bregman