Konstantina Christakopoulou Liang Zeng Group G21 Big Data: New Tricks for Econometrics Varian, Hal R. "Big data: New tricks for econometrics." The Journal of Economic Perspectives (2014): 3-27. Konstantina Christakopoulou Liang Zeng Group G21 Related to the Chapter 28: Data Mining
Motivation. Machine Learning for Economic Transactions: Linear Regression is not Enough! Big data size A lot of features: Choose variables Relationships are not only linear!!
Connection to the Course: Decision Trees e.g ID3 Challenges of ID3: Cannot handle continuous attributes Prone to outliers 1. C4.5, Classification And Regression Trees (CART) can handle: + continuous and discrete attributes + handle missing attributes + over-fitting by post-pruning 2. Random Forests: Ensemble of decision stumps. Randomization (choosing sample + choosing attributes) leads to better accuracy!
ID3 Decision Tree
Classification and Regression Trees(CART) Classification tree is when the predicted outcome is the class to which the data belongs. Regression tree is when the predicted outcome can be considered a real number (e.g. the age of a house, or a patient’s length of stay in a hospital).
Classification and Regression Trees(CART) Predict Titanic survivors using age and class
Classification and Regression Trees(CART) A CART for Survivors of the Titanic using R language
Random Forests
Random Forests Decision Tree Learning + Many decision trees + One Tree Choose a bootstrap sample and start to grow a tree At each node: Choose random sample of predictors to make the next decision Repeat many times to grow a forest of trees For prediction: have each tree make its prediction and then a majority vote. Decision Tree Learning + Many decision trees + One Tree + Each DT on a random subset of samples + On all learning samples + Reduce the effect of outliers (no overfitting) + Prone to distortions e.g outliers Random Forest
Boosting, Bagging, Bootstrap Randomization can help! Bootstrap: choose (with replacement) a sample Bagging: averaging across models estimated with several bootstraps Boosting: repeated estimation where misclassified observations are given an increasing weight. Final is an average
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