(5)To ensure harmonisation of the calculation of the stress scenario risk measures across institutions in the Union, it is necessary to specify how institutions should identify the stress period. Those specifications should be proportionate to the purpose, and should neither require an excessive computational effort, nor the implementation of specific pricing methods. The global financial crisis of 2007–2008 has been a major stress event for the financial system. The stress period to be identified should therefore start at least from 1 January 2007. To ensure that the stress period remains relevant to an institution’s trading portfolio, institutions should periodically review that stress period. However, to limit the administrative burden on institutions, it should be only required that the frequency of such review follows at least the same quarterly frequency as the corresponding supervisory reporting.