===== Threshold Value =====

The **threshold value** in CUSUM analysis defines the alert level at which the cumulative sum of deviations signals a statistically significant change in performance.

It serves as a boundary for action:
  * When the CUSUM curve **crosses the threshold**, it may indicate deteriorating performance (e.g., rising complication rate).
  * Staying **below the threshold** suggests performance remains within acceptable limits.

==== How It’s Determined ====

Threshold values can be:
  * **Statistical**, based on type I/II error probabilities and decision intervals (commonly used in industrial applications).
  * **Empirical**, based on institutional experience or expert consensus.
  * **Graphical**, set arbitrarily for visual feedback (e.g., 2.5 in our ICP example).

In our analysis of ICP monitor placement, we used a **threshold of 2.5** to flag deviations from the acceptable complication rate of 10%. This value is not fixed and can be adjusted depending on:
  * Procedure complexity
  * Acceptable risk tolerance
  * Training level of the surgeon

==== Clinical Application ====

Crossing the threshold may prompt:
  * Case review or morbidity and mortality (M&M) analysis
  * Temporary increase in supervision or training
  * Modification of technique, workflow, or equipment

Using CUSUM with a clearly defined threshold value transforms raw outcome data into a **real-time decision-support tool** for improving patient safety and clinical performance.
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Institutions may modify the threshold value based on:
  * [[Historical complication rate]]s
  * [[Supervision level]]
  * [[Case complexity]]
  * [[Acceptable risk policy]]