Statistical Thinking for the 21st Century

Poldrack is a Stanford neuroscientist who wrote an open-source statistics textbook because he was tired of what was available for his own students. The book covers the fundamentals — probability, hypothesis testing, regression — with modern emphasis on effect size, Bayesian reasoning and reproducibility. For product direction it is the most rigorous free option on the shelf: it does not shy away from formalism, but it does not hide behind it either. The book is continuously updated, which is itself a small lesson about how serious educational material travels in the open-source era. Pair it with Wheelan for the intuition layer and Gill for a four-page Bayesian warm-up.