Unifying the study of background dynamics and perturbations in   $f(R)$-gravity
  In this paper we show how the covariant gauge invariant equations for the evolution of scalar, vector and tensor perturbations for a generic $f(R)$-gravity theory can be recast in order to exploit the power of dynamical system methodology. In this way, recent results describing the dynamics of the background FRW model can be easily combined with these equations to reveal important details pertaining to the evolution of cosmological models in fourth order gravity. 
Sante Carloni, Kishore N. Ananda, Peter K. S. Dunsby, Mohamed E. S.   Abdelwahab