The percentage of relevant threats mitigated is the best key control indicator (KCI) to determine the effectiveness of an intrusion prevention system (IPS), because it measures how well the IPS is performing its intended function of preventing unauthorized access or attacks. The percentageof system uptime is not a good KCI, because it does not reflect the quality or accuracy of the IPS. The total number of threats identified is not a good KCI, because it does not indicate how many of those threats were actually prevented by the IPS. The reaction time of the system to threats is not a good KCI, because it does not measure the impact or severity of the threats that were prevented or not prevented by the IPS. References = CRISC: Certified in Risk & Information Systems Control Sample Questions2