Rigorous introduction to statistical concepts that underpin econometrics. Course emphasizes conceptual understanding, uses mathematics to illustrate ideas, and applies ideas to examples from economics broadly construed. Students analyze data to reinforce understanding. Topics include experimental and non-experimental research designs; modern approaches to summarizing data; random variables, probability, expectations, density and distribution functions; sampling; estimation; inference and hypothesis testing; introduction to linear regression. First course in two-semester econometrics sequence. Prerequisite: Mathematics 21, 106L,111L, 112L, 121, 122, 122L, 202, 202D, 212, or 222.