===== Historical Complication Rate =====

The **historical complication rate** is the average rate of adverse outcomes observed in a specific procedure over a defined period. It serves as the foundation for setting the **reference value (k)** and the **CUSUM threshold** in surgical performance monitoring.

==== Purpose ====

In CUSUM analysis, this historical rate provides a **realistic performance benchmark**, allowing current outcomes to be compared meaningfully with past institutional or published data.

==== How It's Calculated ====

To determine the historical complication rate for intracranial pressure (ICP) monitor placement:

  * Review all relevant cases over the past 1–3 years.
  * Count the total number of complications (e.g., infection, hemorrhage, malposition).
  * Divide by the total number of procedures performed.

Example:
  * 12 complications over 120 ICP placements  
  * Historical complication rate = 12 / 120 = **10%** → ''k = 0.1''

==== Why It Matters ====

  * Establishes the **target** used in the CUSUM equation (reference value ''k'').
  * Serves as a baseline to detect improvements or deteriorations in current performance.
  * Helps differentiate between **expected risk** and **performance-related issues**.

==== Sources of Historical Data ====

  * Institutional surgical audit records
  * National registries or multicenter studies
  * Peer-reviewed literature (e.g., complication rates from similar patient populations)

==== Best Practices ====

  * Use **local data** when available for the most accurate benchmark.
  * Update the historical rate **periodically** to reflect improvements in technique or changes in patient population.
  * Stratify data by factors like **procedure type**, **surgeon experience**, or **patient complexity** when possible.

By grounding your CUSUM analysis in real-world historical data, you ensure that the performance thresholds are both **clinically meaningful** and **fairly applied**.