  A system is in a self-organized critical state if the distribution of some
measured events (avalanche sizes, for instance) obeys a power law for as many
decades as it is possible to calculate or measure. The finite-size scaling of
this distribution function with the lattice size is usually enough to assume
that any cut off will disappear as the lattice size goes to infinity. This
approach, however, can lead to misleading conclusions. In this work we analyze
the behavior of the branching rate sigma of the events to establish whether a
system is in a critical state. We apply this method to the
Olami-Feder-Christensen model to obtain evidences that, in contrast to previous
results, the model is critical in the conservative regime only.
