(12)Operational risk modelling is a relatively new and evolving discipline. Accordingly, Article 322 of Regulation (EU) No 575/2013 grants significant flexibility to institutions in building the operational risk measurement system for calculating the AMA own funds requirements. Such flexibility, however, should not result in significant differences across institutions with regard to the key components of the measurement system, including the use of internal data, external data, scenario analysis and business environment and internal control factors (known and referred to as ‘the four elements’), the core modelling assumptions that permit capturing severe tail events and the related risk drivers (the building of the calculation data set, the granularity, the identification of the loss distributions and the determination of aggregated loss distributions and risk measures) or the expected loss, the correlation and the criteria for capital allocation which should ensure a measurement system's internal consistency. Therefore, with the view to ensuring that the risk measurement system is methodologically well founded, comparable across the institutions, effective in capturing the institutions' actual and potential operational risk and reliable and robust in generating AMA regulatory capital requirements, the methodology for AMA assessment should provide that the same criteria and requirements are applied by the competent authorities across the Union. The AMA assessment methodology should also take into consideration the idiosyncratic components of operational risk that are related to the institutions' different size, nature and complexity.