AdaBoost is a machine learning algorithm that uses multiple weak learners to create a strong learner. It works by assigning higher weights to misclassified examples from previous iterations and runs multiple iterations, each time adding a new weak learner that focuses on the examples with higher weights. The document presents an experiment using AdaBoost with decision stumps on a cancer dataset, finding a classification accuracy of 93.12% compared to 92.97% for decision stumps alone. ROC/AUC analysis showed AdaBoost with an AUC of 0.975 outperforming decision stumps with an AUC of 0.911, demonstrating that AdaBoost can create a more effective classifier than a single weak learner.

1. An Overview of Adaptive Boosting – AdaBoost
Presented By
Kato Mivule
Dr. Manohar Mareboyana, Professor
Data Mining - Spring 2013
Computer Science Department
Bowie State University
An Overview of AdaBoost
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2. OUTLINE
• Introduction
• How AdaBoost Works
• The experiment
• Results
• Conclusion and Discussion
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An Overview of AdaBoost

3. Adaptive Booting – AdaBoost
• Adaptive Boosting (AdaBoost) was proposed by Freund and Schapire (1995).
• AdaBoost is a machine learning classifier that uses several iterations by adding
weak learners to generate a new learner with improved performance.
• AdaBoost is adaptive in that with each iteration, a new weak learner is added
to the AdaBoost classifier by fine-tuning weights with priority given to
misclassified data in prior iterations.
• AdaBoost is less vulnerable to over-fitting but prone to noise and outliers.
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An Overview of AdaBoost

4. AdaBoost Fit Ensemble
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An overview of the AdaBoost Fit Ensemble procedure.
An Overview of AdaBoost

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An Overview of AdaBoost

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An Overview of AdaBoost

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An Overview of AdaBoost

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An Overview of AdaBoost

9. How AdaBoost Works – Weak Learners
• Decision Stump
• For this overview, we choose Decision Stumps as our weak learner.
• The Decision Stump generates a decision tree with only one single split.
• The resulting tree can be used for classifying unseen (untrained) instances.
• The leaf nodes is the class name.
• A non-leaf node is a decision node.
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An Overview of AdaBoost

10. How AdaBoost Works – Weak Learners
• How a Decision Stump chooses the best attributes:
• Information gain: attribute with lowest info gain is chosen.
• Gain ratio.
• Gini index.
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An Overview of AdaBoost

11. AdaBoost – the experiment
• For illustration purposes, we utilized Rapid Miner’s AdaBoost functionality
• We used a UCI Cancer dataset with 643 data points.
• We employed a 10 fold cross validation.
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An Overview of AdaBoost

12. AdaBoost – the experiment
• We used Rapid Miner’s Decision Stump as our weak learner.
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An Overview of AdaBoost

13. AdaBoost – Results
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Generated AdaBoost Model
The following AdaBoost Model was generated:
AdaBoost (prediction model for label Class)
Number of inner models: 3
Embedded model #0 (weight: 2.582):
Uniformity of Cell > 3.500: 4 {2=11, 4=202}
Uniformity of Cell ≤ 3.500: 2 {2=433, 4=37}
Embedded model #1 (weight: 1.352):
Uniformity of Cell Shape > 1.500: 4 {2=100, 4=237}
Uniformity of Cell Shape ≤ 1.500: 2 {2=344, 4=2}
Embedded model #2 (weight: 1.016):
Clump Thickness > 8.500: 4 {2=0, 4=83}
Clump Thickness ≤ 8.500: 2 {2=444, 4=156}
An Overview of AdaBoost

14. AdaBoost – Results
• AdaBoost using Decision Stumps – classification accuracy at 93.12%.
• Decision Stump with out AdaBoost – classification accuracy at 92.97%.
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An Overview of AdaBoost

15. AdaBoost – the results
• AdaBoost Confusion Matrix – Classification accuracy at 93.12%
• Decision Stump Confusion Matrix – Classification accuracy at 92.97%
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An Overview of AdaBoost

16. AdaBoost – the results
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An Overview of AdaBoost
The Receiver Operating Characteristic
(ROC):
•The ROC shows the false positive rate on X-
axis (specificity), the probability of target = 1
when its true value is 0.
•The true positive rate on Y-axis (sensitivity),
the probability of target=1 when its true value
is 1.
•For an ideal situation, the curve rises fast to
the top-left indicating that the model correctly
made the predictions.
Area Under the Curve (AUC):
•AUC shows how the classifier will rank a
randomly chosen positive instance higher
than a randomly chosen negative instance.
•The AUC calculates total performance of
classifier.
•Higher AUC indicates better performance.
•0.50 AUC indicates random performance.
•1.00 AUC indicates perfect performance
weight:
The ROC/AUC plot for AdaBoost – with AUC of 0.975.
The ROC/AUC plot for Decision Stamp – with AUC of 0.911.

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CONCLUSION
• As shown in the preliminary results, AdaBoost performs better
than Decision Stump.
• However, much of the success for the AdaBoost will depend
largely on fine-tuning parameters in the machine learning
classifier and the weak learner that is chosen.
An Overview of AdaBoost

18. References
1. Y. Freund and R. E. Schapire, "A Decision-Theoretic generalization of On-Line learning and an application to boosting," Journal of
Computer and System Sciences, vol. 55, no. 1, pp. 119-139, Aug. 1997.
2. T. G. Dietterich, "Ensemble methods in machine learning," Lecture Notes in Computer Science, vol. 1857, pp. 1-15, 2000.
3. Kato Mivule, Claude Turner, Soo-Yeon Ji, Towards A Differential Privacy and Utility Preserving Machine Learning Classifier, Procedia
Computer Science, Volume 12, 2012, Pages 176-181
4. T. Fawcett, “An introduction to ROC analysis.”, Pattern recognition letters, vol. 27, no.8, 2006, Pages 861-874.
5. K. Bache and M. Lichman, “Breast Cancer Wisconsin (Original) Data Set - UCI Machine Learning Repository.” University of
California, School of Information and Computer Science., Irvine, CA, 2013.
6. MATLAB, “AdaBoost - MATLAB.” Online, Accessed: May 3rd 2013, Available: http://www.mathworks.com/discovery/adaboost.html.
7. MATLAB, “Ensemble Methods :: Nonparametric Supervised Learning (Statistics Toolbox™).” Online, Accessed: May 3rd 2013,
Available: http://www.mathworks.com/help/toolbox/stats/bsvjye9.html#bsvjyi5.
8. ROC Charts, “Model Evaluation – Classification” Online, Accessed May 3rd 2013, Available: http://chem-
eng.utoronto.ca/~datamining/dmc/model_evaluation_c.htm
9. MedCalc, “ROC curve analysis in MedCalc”, Online, Accessed May 3rd 2013, Available: http://www.medcalc.org/manual/roc-
curves.php
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An Overview of AdaBoost

19. THANK YOU.
Contact: kmivule at gmail dot com
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An Overview of AdaBoost