Equivalence of conditional and external field ensembles in absorbing-state phase transitions

I comment on the relation between two sampling methods for absorbing-state models. It is shown that a certain ensemble without external field conditional to activity coincides with the unconditional ensemble for sufficiently small external field. The actual physical processes involved are identical and the derivation of the identity of the scaling behavior relies on a single (established) scaling law. While the conditional ensemble by construction does not contain information about the system with large external field, it contains all the information about the limit of vanishing external field and about the vicinity of the critical point: finite size scaling as well as critical scaling in the temperature-like variable or in (small) external field.