Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

probability versus statistics

Probability reasons forward, from a known population to a sample; statistics reasons backward, from an observed sample to an unknown population.