A/B testing, also known as split or bucket testing, is a scientific method used to measure causality by comparing two groups: a test group receiving a new feature and a control group with the base version. This method, which is widely adopted in clinical trials and digital marketing, helps organizations like Facebook, Netflix, and Amazon optimize products by determining the impact of changes on user engagement metrics, while controlling for confounding factors through randomization. The process involves statistical testing to identify if differences between groups are statistically significant, with results considered significant if they exceed a set threshold, usually 95%. A/B testing offers a comprehensive view by evaluating primary, secondary, and ecosystem effects, allowing businesses to make informed decisions, and is supported by platforms like Statsig, which makes the process accessible to all levels of experimenters.