(11)As the rating systems are the core of the IRB Approach, and their quality may impact significantly the level of own funds requirements, the performance of the rating systems should be regularly reviewed. Given that estimates of risk parameters have to be subject to review at least annually and that rating systems should be regularly assessed by competent authorities and by the internal audit function, and given that, in order for this task to be performed, input from the validation function is necessary, it is appropriate to verify that the validation of the performance of the rating systems covering material portfolios and back-testing of all other rating systems is performed at least annually.