# Statistical Learning: 6.7 The Lasso | Summary and Q&A

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October 7, 2022
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Stanford Online
Statistical Learning: 6.7 The Lasso

## TL;DR

The lasso is a technique for shrinking coefficients in regression and selecting important variables, using an absolute value penalty instead of sum of squares.

## Questions & Answers

### Q: How does the lasso differ from ridge regression?

The lasso and ridge regression are similar techniques for shrinking coefficients, but the lasso uses an absolute value penalty instead of a sum of squares. This allows the lasso to set coefficients exactly to zero in situations where they are not important.

### Q: What is the significance of sparsity in the lasso?

The lasso produces sparse models, which means they only involve a subset of variables. This is valuable in practical applications where selecting fewer variables is desired, such as in medical testing where expensive tests involving many variables are not feasible.

### Q: How is the tuning parameter lambda chosen in the lasso?

The tuning parameter lambda controls the level of shrinkage in the lasso. It needs to be chosen in order to find the best model. One common approach is to use cross-validation to evaluate the performance of different lambdas and select the one that minimizes prediction error.

### Q: Why has the lasso gained popularity in recent years?

The lasso has become popular due to advancements in computation and the development of convex optimization algorithms. This has made it easier to solve the lasso problem even for large datasets with many variables, making it a highly useful tool in various fields.

## Summary & Key Takeaways

• The lasso is a technique that shrinks coefficients towards zero using an absolute value penalty, allowing for variable selection and sparse models.

• The sparsity of the lasso allows for the selection of a subset of variables, making it useful in practical applications where fewer variables are preferred.

• The lasso can be used alongside ridge regression, and the choice between the two depends on the sparsity of the true model.

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