fix broken docs link

Author: Ayzel0

docs/stats-engine/methodologies/cuped.md

@@ -14,7 +14,7 @@ CUPED (short for Controlled-experiment Using Pre-Existing Data) is a technique w
 
 Our Cloud product uses a 7-day window for CUPED calculation. For Warehouse Native customers, a 7-day window is recommended, but you have the flexibility to customize it to any length.
 
-See more at the [Variance Reduction](../variance-reduction.md) page.
+See more at the [Variance Reduction](https://docs.statsig.com/experiments/statistical-methods/variance-reduction) page.
 
 ## CUPED for Simple Aggregations