(a)they shall use an expert-based approach using qualitative and quantitative information available to identify a loss due to a change in the values taken by the non-modellable risk factors that will not be exceeded with a level of certainty equal to 99,95 % on a 10 business day horizon in a future period of financial stress equivalent to the stress period for the non-modellable risk factors. When doing so, institutions shall take into account the skewness and the excess kurtosis that may characterise the returns of the non-modellable risk factors in a period of financial stress and shall justify any distributional or statistical assumptions taken for identifying that loss;