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

finite population correction

The factor that shrinks the standard error when sampling without replacement from a finite population, always at most 1.

$\sqrt{(N-n)/(N-1)}$ .