You have a sample of data and you want to know something about the average of a larger group. Maybe it’s the average battery life of a new phone, the mean improvement in test scores after a study program, or whether a new fertilizer really makes plants taller. This chapter teaches you honest ways to answer these questions. You’ll learn about t‑tests and confidence intervals for one mean, for the difference between two independent means, and for paired data. By the end, you’ll know not just which test to run, but why it works and what its limits are.