Because that&#x27;s a lot harder. At VWO we do exactly this in our new SmartStats tool - we believe Bayesian stats are far more intuitive to the end user. But we&#x27;ve got a whole compute cluster running these calculations 24&#x2F;7. For comparison, our old frequentist calculations were done in PHP at page render time.<p>A formula that can be easily plugged into Excel does have value over a formula that requires someone to write a python script and do a monte carlo simulation.<p>Evan&#x27;s method is also nice in that it doesn&#x27;t require a lot in terms of knowing your (possibly very small) conversion rate ahead of time.