# Holdout test

URL: https://idukki.io/glossary/holdout-test
Category: Metrics
Also called: A/B holdout, control arm

The only way to measure UGC lift defensibly. Serve UGC to half of PDP visitors, hide it from the other half, measure the delta. Anyone reporting UGC lift without a holdout has assumed it, not measured it.

## Related terms

- [Lift / incremental lift](https://idukki.io/glossary/lift)
- [CR / Conversion rate](https://idukki.io/glossary/conversion-rate)