Measure Theory

A graduate-level textbook that most product directors will never read cover to cover and should still know exists. Measure theory is the mathematical foundation under probability, statistics and any rigorous claim you make from data — sets, sigma-algebras, integrals against measures. Halmos's prose is legendary for its economy: few mathematicians have written with less waste. You keep this book on the shelf for two reasons: to humble any intuition about "what the data says" before checking what the data can actually support, and because a product director who respects the distance between everyday statistics and its real foundations argues differently in the rooms where that distance matters.