  A generalized fluctuation-response relation is found for thermal systems
driven out of equilibrium. Its derivation is independent of many details of the
dynamics, which is only required to be first-order. The result gives a
correction to the equilibrium fluctuation-dissipation theorem, in terms of the
correlation between observable and excess in dynamical activity caused by the
perturbation. Previous approaches to this problem are recovered and extended in
a unifying scheme.
