Nonuniversality and critical point shift in systems with infinitely many absorbing configurations

A detailed study of critical spreading in the one-dimensional pair contact process is performed using a recently devised reweighting method. The results confirm the validity of a generalized hyperscaling relation among the (nonuniversal) spreading exponents, and support the assertion that the critical point location does not depend on the particle density \phi. It appears that the exponents z and delta+eta, once thought to be invariant, exhibit a systematic dependence on \phi.