  The question of universality class of pair contact process with diffusion
(PCPD) is revisited with an alternative approach. We study persistence in
Generalized Pair-Contact Process with diffusion (GPCPD) introduced by Noh and
Park, (Phys. Rev. E 69,016122(2004)). This model allows us to interpolate
between directed percolation (DP) and PCPD universality classes. We find that
transition to nonzero persistence is at same parameter value as transition to
zero number density. We obtain finite size scaling and off-critical scaling
collapse for persistence and find critical exponents by fitting
phenomenological scaling laws to persistence. While the dynamic scaling
exponent $z$ varies continuously in GPCPD, the correlation-time exponent
$\nu_\parallel$ matches with directed percolation universality class.
