Randomized Experiments — The Gold Standard, and Your A/B Test
The most reliable way to establish causation is almost embarrassingly simple: flip a coin to decide who gets the treatment. Randomization is the one technique that defeats confounding completely — including confounders you never thought of — which is why the randomized controlled trial is the gold standard of causal evidence and why the A/B test is the most powerful tool an engineer has. This post explains why randomization works its magic, and the many ways real experiments still go wrong.
The most reliable way to establish causation is almost embarrassingly simple: randomize. Why randomization defeats all confounders at once (even unknown ones), why the A/B test is a genuine causal tool, and the many ways real experiments still go wrong (peeking, power, interference, broken randomization).