What is Lasso (Least Absolute Shrinkage And Selection Operator) ?

Lasso (Least Absolute Shrinkage And Selection Operator) in statistics and machine learning is a regression analysis method that performs both variable selection and regularization in order to enhance the prediction accuracy and interpretability of the statistical model it produces. Lasso was originally formulated for least squares models and this simple case reveals a substantial amount about the behaviour of the estimator, including its relationship to ridge regression and best subset selection and the connections between lasso coefficient estimates and so-called soft thresholding. It also reveals that (like standard linear regression) the coefficient estimates need not be unique if covariates are collinear. Though originally defined for least squares, lasso regularization is easily extended to a wide variety of statistical models including generalized linear models, generalized estimating equations, proportional hazards models, and M-estimators, in a straightforward fashion. Lasso’s ability to perform subset selection relies on the form of the constraint and has a variety of interpretations including in terms of geometry, Bayesian statistics, and convex analysis. Lasso is able to improve prediction accuracy and reduce overfitting by effectively choosing a simpler model that does not include those coefficients.

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