A key performance indicator (KPI) is a measurable value that demonstrates how effectively an organization is achieving its objectives. In the context of disaster recovery planning (DRP), a KPI should reflect the ability of the organization to recover its critical business processes and applications within the predefined time frames and service levels. One of the most important KPIs for DRP is the percentage of applications that met the recovery time objective (RTO) during DRP testing. The RTO is the maximum acceptable length of time that a business process or application can be down after a disaster. By measuring the percentage of applications that met the RTO during DRP testing, the organization can evaluate the performance and reliability of its DRP, identify any gaps or weaknesses, and implement corrective actions to improve its readiness and resilience. The other options are not the best KPIs for DRP, as they do not directly measure the effectiveness of the recovery process. The number of users that participated in the DRP testing is a measure of the involvement and awareness of the staff, but not of the outcome of the testing. The number of issues identified during DRP testing is a measure of the quality and completeness of the DRP, but not of the actual recovery time. The percentage of issues resolved as a result of DRP testing is a measure of the improvement and maturity of the DRP, but not of the current recovery capability. References = Risk and Information Systems Control Study Manual, 7th Edition, Chapter 3, Section 3.2.3.3, Page 138.