Final answer:
After performing a quantitative risk analysis and applying a countermeasure, the Annualized Rate of Occurrence (ARO) is the factor that would change. The ARO adjusts as the countermeasure modifies the likelihood of the threat materializing within a year, affecting the overall risk level.
Step-by-step explanation:
When you select a countermeasure after performing a basic quantitative risk analysis and re-calculate, the factor that will change is the Annualized Rate of Occurrence (ARO). The Exposure Factor (EF), Asset Value, and Single Loss Expectancy (SLE) typically remain the same since these are inherent characteristics of the asset and its vulnerabilities. However, the ARO changes because the implementation of a countermeasure affects the likelihood of the risk occurring within a given year.
Risk analysis aims to gauge the potential loss or impact a threat can have on an asset. When a countermeasure is applied, it addresses the vulnerability, thereby reducing either the impact or the frequency of the threat, which in this case is reflected by the decrease in ARO. This is important because a lower ARO implies that the expected frequency of losses due to a threat is reduced, which, consequently, lowers the Annualized Loss Expectancy (ALE).
The key to effective risk management involves not just identifying risks but also implementing the correct countermeasures to mitigate them cost-effectively. This includes weighing the costs of the countermeasures against the risk reduction they offer. Therefore, understanding how different factors in risk analysis are affected by the implementation of countermeasures is critical in making informed decisions about risk management.