Bayesian Experiments
Bayesian Testing in Statsig
Experiments are frequentist by default. To switch to Bayesian mode, go to Advanced Settings.
The experiment type cannot be modified once the experiment starts.
Deep dive analysis should also reflect Bayesian statistics
Informed Bayesian
Bayesian experiments allow you to specify a prior belief on the relative average treatment effect. Statsig will combine the prior distribution with the observed data to display the prior-adjusted results. You can enable this by selecting the option to "use informative priors".
Implementation Details
Denote as the prior distribution, where is the average treatment effect and is the standard error. Similarly, as the observed distribution.
The posterior distribution is then calculated as
If the prior is not specified, the is represented as .
Bayesian Statistics
Bayesian A/B tests have a glossary that are different from the frequentist framework and often believed to be more intuitive in communication to non-technical audience.
- Credible Interval: the interval which we believe contains the true parameter at the given probability
- Chance to Beat: the probability that the test is better than control
- Expected Loss: the average potential risk if you ship test