Do school vouchers really help inner city students become better educated? Do gun control laws really make society safer? This course examines how scientists reason about causal claims like these. It considers use of scientific statistical data that informs our public policy debates. The course uses an interactive, web-based text and exams. In addition, there is an on-line virtual "causality lab" in which students will set up, run, and then analyze simulated experiments. They will construct causal theories, use the lab to derive predictions from these theories, and then test the predictions against the simulated data. While course materials are delivered on-line.