  The fundamental plane of black hole activity is a non-linear correlation
among radio core luminosity, X-ray luminosity and mass of all accreting black
holes, both of stellar mass and supermassive, found by Merloni, Heinz and Di
Matteo (2003) and, independently, by Falcke, Koerding and Markoff (2004). Here
we further examine a number of statistical issues related to this correlation.
In particular, we discuss the issue of sample selection and quantify the bias
introduced by the effect of distance in two of the correlated quantities. We
demonstrate that the fundamental plane relation cannot be a distance artifact,
and that its non-linearity must represent an intrinsic characteristic of
accreting black holes. We also discuss possible future observational strategies
to improve our understanding of this correlation.
