Linear Algebra Formulas for Econometrics

Econometrics is fundamental to many of the problems that data scientists care about, and it requires many skills. There's philosophical skill, for thinking about whether fixed effects or random effects models are more appropriate, for example, or what the direction of causality in a particular problem is. There's some coding, including knowing the right commands to interact with statistical programs like Stata or R, and how to interpret their output. There's the intuition to know which policy issues are worth researching, the political skill to obtain data or grant money, even the writing skill to communicate ideas. And "beneath" it all there is linear algebra: matrix formulas for the estimators that are reported, interpreted, and acted on.