(as others have mentioned) Optimizely&#x27;s newer engine uses ideas like Wald&#x27;s sequential analysis.  Here is my article on the topic: <a href="http:&#x2F;&#x2F;www.win-vector.com&#x2F;blog&#x2F;2015&#x2F;12&#x2F;walds-sequential-analysis-technique&#x2F;" rel="nofollow">http:&#x2F;&#x2F;www.win-vector.com&#x2F;blog&#x2F;2015&#x2F;12&#x2F;walds-sequential-anal...</a> .