In performing Human Reliability Analysis (HRA), the environmental and personal factors impact on human performance and enhance or degrade the human error probability (HEP). Their modelling and quantification is one of the most complex issues in the HRA field, to which many researchers recently are concentrating their efforts. This paper focuses on the eight performance shaping factors (PSFs), used in the Simulator for Human Error Probability Analysis (SHERPA), in order to understand how they affect HEP, considering especially their mutual interactions. The one-factor-at-atime method was used to assess singularly the levels of each factor, while the analysis of variance allowed to realize if there is more or less dependence between them. The...