Supervision level refers to the degree of direct oversight provided to a surgeon—typically a resident or junior attending—during a procedure. It is a critical factor when interpreting CUSUM results and setting appropriate thresholds or reference values.

• Direct supervision: A senior surgeon is physically present and guiding the procedure step-by-step.
• Indirect supervision: A supervisor is available on-site but not scrubbed in; the procedure is performed independently.
• Unsupervised (autonomous): The operator performs the procedure independently, without on-site backup.

• With direct supervision, the expected complication rate (k) should be lower, and the alert threshold stricter, since expert guidance minimizes error.
• With indirect or no supervision, a slightly higher k or more forgiving threshold may be appropriate to account for operator learning or complexity.

Example:

• For ICP monitor placement under direct supervision → k = 0.08, threshold = 2.0
• For independent placements by senior residents → k = 0.12, threshold = 2.5

CUSUM charts stratified by supervision level allow:

• Tailored feedback to individual trainees
• Identification of readiness for progressive autonomy
• Adjustment of supervision strategies based on real-time performance
• Objective support for credentialing and privileging decisions

By incorporating supervision level into CUSUM analysis, training programs can make more nuanced, fair, and accurate judgments about performance and progression.