A statistical analysis comparing the number of CREME-96 worst-week environments to a space environment particle flux data analysis and the PSYCHIC model is presented. This analysis provides an indication of the number of worst-week environments that are required to obtain a particular confidence level and determine the associated risk of a destructive single event effect over a mission but highlights the drawback of such an approach compared to using a statistical model. A method for direct assessment of the number of Single Event Effects expected specific to components and shielding geometries using the European Space Agency SEPEM system is also presented.