How CUPED increases statistical power in experiments

Tests your grasp of variance reduction in A/B testing. Explain how CUPED uses correlated pre-experiment data to reduce outcome variance, increasing statistical power. A red flag is confusing it with simpler difference scores, which can actually increase noise.
Tests your grasp of advanced statistical techniques for A/B testing, specifically variance reduction to increase an experiment's power. A strong answer explains that CUPED uses a pre-experiment covariate (X) correlated with the outcome metric (Y) to create an adjusted metric with lower variance (reduced by a factor of 1-ρ²), making small effects easier to detect. It's an application of ANCOVA and is superior to simple difference scores. A red flag is confusing it with difference-in-differences, which can harm power if correlation is low.
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- #a/b testing
- #statistics
- #metrics
- #experimentation
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