Changes in methods used to calculate probability present the greatest challenge for an IT risk practitioner who wants to report on trends in historical IT risk levels, as they may introduce inconsistency and incomparability in the risk assessment results over time. Probability is a key factor in determining the level and priority of IT risks, and different methods may produce different values for the same risk scenario. For example, some methods may use historical data, expert judgment, or simulation techniques to estimate the likelihood of a risk event. If the methods used to calculate probability change frequently or vary across different business units or processes, the IT risk practitioner may face difficulty in aggregating, normalizing, and reporting the risk levels and trends. The other options are not the greatest challenges for reporting on trends in historical IT risk levels, although they may pose some difficulties or limitations. Qualitative measures for potential loss events are subjective and imprecise, but they can stillprovide a relative ranking of risks and their impacts. Changes in owners for identified IT risk scenarios may affect the accountability and responsibility for managing the risks, but they do not necessarily affect the risk levels or trends. Frequent use of risk acceptance as a treatment option may indicate a high risk appetite ortolerance, but it does not prevent the IT risk practitioner from reporting on the risk levels or trends. References = Risk and Information Systems Control Study Manual, Chapter 5: Risk and Control Monitoring and Reporting, page 181.