Econometrics has a reputation for frightening students. Equations appear, Greek letters multiply, matrices arrive without warning, and suddenly a simple economic question seems to require a small laboratory of mathematics. But the real difficulty is rarely the mathematics itself—it is understanding why the mathematics is there. This book reverses the usual order. Instead of beginning with equations and asking students to discover their meaning later, it begins with an economic question: Does education affect income? From this deceptively simple question emerges the entire econometric framework. Education is difficult to interpret because people differ in ability, family background, motivation, health, networks, geography, and countless other factors. An instrumental variable—distance to a university—provides a way to find variation in education that can help us identify a causal effect. What begins with a single coefficient gradually becomes a complete econometric framework, with every symbol translated into ordinary language. The mathematics does not disappear; instead, it becomes understandable and purposeful. The aim is simple: to make the mathematics feel inevitable. Once the economic question is clear, the equation should feel like the obvious sentence written in mathematical shorthand. By the end, students should be able to approach any unfamiliar regression and ask five essential questions: What are we trying to explain? What is doing the explaining? What is the coefficient saying? Why might it be wrong? And what source of variation could make it credible?
