Defining a clear and realistic outcome target is fundamental for the validity of any CUSUM analysis. The target represents the acceptable performance level or complication rate that serves as a benchmark for comparison.

In this analysis, we selected a target complication rate of 10% (k = 0.1) for ICP monitor placements, based on:

• Published literature on acceptable complication rates for external ventricular drains and ICP bolts.
• Internal quality control data from our institution.
• Consensus among experienced neurosurgeons in the department.

The outcome target must strike a balance between being challenging enough to drive improvement and realistic enough to reflect clinical complexity.

Targets may vary depending on:

• Procedure type (e.g., tumor resection vs. shunt placement)
• Patient population (e.g., pediatric vs. adult)
• Institutional context (e.g., high-volume center vs. low-resource setting)

Outcome targets can also be dynamic. As surgical teams gain experience or new techniques are adopted, the acceptable rate may be adjusted downward to reflect higher expected standards.