Explanation
The organizational risk register is the most useful for an information security manager when determining the need to escalate an incident to senior management because it contains a list of identified risks to the organization, their likelihood and impact, and their predefined risk thresholds or targets, which can help the information security manager assess the severity and urgency of the incident and decide whether it requires senior management's attention or action. Incident management procedures are not very useful for this purpose because they do not provide any specific criteria or guidance on when to escalate an incident to senior management. Incident management policy is not very useful for this purpose because it does not provide any specific criteria or guidance on when to escalate an incident to senior management. System risk assessment is not very useful for this purpose because it does not reflect the current risk exposure or status of the organization as a whole. References:
https://www.isaca.org/resources/isaca-journal/issues/2016/volume-6/how-to-measure-the-effectiveness-of-inform
https://www.isaca.org/resources/isaca-journal/issues/2017/volume-5/incident-response-lessons-learned