An Objective Definition of Damage Spreading - Application to Directed   Percolation
  We present a general definition of damage spreading in a pair of models. Using this general framework, one can define damage spreading in an objective manner, that does not depend on the particular dynamic procedure that is being used. The formalism is applied to the Domany-Kinzel cellular automaton in one dimension; the active phase of this model is shown to consist of three sub-phases, characterized by different damage-spreading properties. 
Haye Hinrichsen, Joshua S. Weitz and Eytan Domany