Ordinary Least Squares
Also called: OLS, least squares regression, linear regression
Ordinary least squares fits a line by minimising the sum of squared residuals — the workhorse estimator of applied economics and finance. Squaring is what makes it tractable and what makes it fragile: large errors dominate the fit, so a handful of outliers can swing a coefficient completely. It is unbiased only when its assumptions hold, and most econometrics is the study of what to do when they don't.
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