  The goal of response theory, in each of its many statistical mechanical
formulations, is to predict the perturbed response of a system from the
knowledge of the unperturbed state and of the applied perturbation. A new
recent angle on the problem focuses on providing a method to perform
predictions of the change in one observable of the system by using the change
in a second observable as a surrogate for the actual forcing. Such a viewpoint
tries to address the very relevant problem of causal links within complex
system when only incomplete information is available. We present here a method
for quantifying and ranking the predictive ability of observables and use it to
investigate the response of a paradigmatic spatially extended system, the
Lorenz '96 model. We perturb locally the system and we then study to what
extent a given local observable can predict the behaviour of a separate local
observable. We show that this approach can reveal insights on the way a signal
propagates inside the system. We also show that the procedure becomes more
efficient if one considers multiple acting forcings and, correspondingly,
multiple observables as predictors of the observable of interest.
