Simple random sampling. You can do anything with meaningful precision -- often at a fraction of the cost. The key insight is you rarely need an exact number, j

Simple random sampling. You can do anything with meaningful precision -- often at a fraction of the cost. The key insight is you rarely need an exact number, just something in the right ballpark. And sometimes that ballpark is surprisingly big. (More advanced sampling methods are basically just variance-reducing techniques which give you better precision at cost or lower cost for the same precision, but the big leap in ROI is learning to sample in the first place.)