1. A method of assessing a power penalty at a given bit error rate of a multimode fiber, comprising: a first step of differential mode delay measurement including measuring a set of elementary fiber responses corresponding respectively to different offset launches of light over the core radius into the multimode fiber; a second step of generating a global fiber response by applying, to the set of elementary fiber responses, a set of weighting coefficients and time delays respectively depending on the different offset launches of the elementary fiber responses; and a third step of computing a parameter representative of a fiber power penalty from the global fiber response; wherein, in the second step of generating a global fiber response, the set of weighting coefficients includes several subsets of weighting coefficients that are time delayed relative to one another, wherein at least one relative time delay is not set to zero, and wherein the weighting coefficients of each subset respectively depend on the different offset launches of the elementary fiber responses.