We consider C 2 families t → ft of C 4 nondegenerate unimodal maps. We study the absolutely continuous invariant probability (SRB) measure µt of ft, as a function of t on the set of Collet-Eckmann (CE) parameters:Upper bounds: Assuming existence of a transversal CE parameter, we find a positive measure set of CE parameters ∆, and, for each t 0 ∈ ∆, a set ∆ 0 ⊂ ∆ of polynomially recurrent parameters containing t 0 as a Lebesgue density point, and constants C ≥ 1, Γ > 4, so that, for every 1/2-Hölder function A,In addition, for all t ∈ ∆ 0 , the renormalisation period Pt of ft satisfies Pt ≤ Pt 0 , and there are uniform bounds on the rates of mixing of f Pt t for all t with Pt = Pt 0 . If ft(x) = tx(1 − x), the set ∆ contains almost all CE parameters.Lower bounds: Assuming existence of a transversal mixing Misiurewicz-Thurston parameter t 0 , we find a set of CE parameters ∆ ′ M T accumulating at t 0 , a constant C ≥ 1, and a C ∞ function A 0 , so that C|t − t 0 | 1/2 ≥ A 0 dµt − A 0 dµt 0 ≥ C −1 |t − t 0 | 1/2 , ∀t ∈ ∆ ′