We have measured the probability distribution function of the ratio R_X = log L_1.4/L_X, where L_1.4/L_X = ν L_ν(1.4 GHz)/L_X(2–10 keV), between the 1.4 GHz and the unabsorbed 2–10 keV luminosities and its dependence on L_X and z. We have used a complete sample of ~1800 hard X-ray selected AGN, observed in the 1.4 GHz band, cross-correlated in order to exclude FR II-type objects, and thus obtain a contemporaneous measure of the radio and X-ray emission. The distribution P(R_X|L_X,z) is shown in Figure 1. Convolution of the distribution P(R_X|L_X,z) with the 2–10 keV X-ray AGN luminosity function from La Franca et al. (2005) and the relations between radio power and kinetic energy from Best et al. (2006) and Willott et al. (1999) allows us to derive the AGN kinetic power and its evolution. As shown in Figure 1, our results are in good agreement with the predictions of the most recent models of galaxy formation and evolution (e.g., Croton et al. 2006), where AGN radio feedback is required to quench the star formation.