In bladed disks' dynamics the so called "mistuning" is the effect of uncertainties which break the ideally tuned configuration imposed at the design stage. Nowadays, the mistuning topic takes a great relevance in the turbomachinery field, since it is associated to a behaviour which is not predictable by analyses done with cyclic symmetry and leads to non conservative results in terms of peak amplitudes at resonance. From a numerical point of view, the study of mistuning requires the simulation of the whole bladed disk and consequently leads to high computational costs: for this purpose it is necessary to develop reduction techniques that must also take into account the perturbation of a design parameter.