如何提高matlab中决策树的准确性

Question

I have a set of data which I classify them in matlab using decision tree. I divide the set into two parts; one training data(85%) and the other test data(15%). The problem is that the accuracy is around %90 and I do not know how I can improve it. I would appreciate if you have any idea about it.

Answer 1

Decision trees might be performing low because of many reasons, one prominent reason which I can think of is that while calculating a split they do not consider inter-dependency of variables or of target variable on other variables. Before going into improving the performance, one should be aware that it shall not cause over-fitting and shall be able to generalize.

To improve performance these few things can be done:

• Variable preselection: Different tests can be done like multicollinearity test, VIF calculation, IV calculation on variables to select only a few top variables. This will lead in improved performance as it would strictly cut out the undesired variables.

• Ensemble Learning Use multiple trees (random forests) to predict the outcomes. Random forests in general perform well than a single decision tree as they manage to reduce both bias and variance. They are less prone to overfitting as well.

• K-Fold cross validation: Cross validation in the training data itself can improve the performance of the model a bit.

• Hybrid Model: Use a hybrid model, ie use logistic regression after using decision trees to improve performance.

Answer 2

I guess the more important question here is what's a good accuracy for the given domain: if you're classifying spam then 90% might be a bit low, but if you're predicting stock prices then 90% is really high!

If you're doing this on a known domain set and there are previous examples of classification accuracy which is higher than yours, then you can try several things:

• K-Fold Cross Validation
• Ensamble Learning
• Generalized Iterative Scaling (GIS)
• Logistic Regression

Answer 3

I don't think you should improve this, may be the data is overfitted by the classifier. Try to use another data sets, or cross-validation to see the more accurate result.

By the way, 90%, if not overfitted, is great result, may be you even don't need to improve it.

Answer 4

You could look into pruning the leaves to improve the generalization of the decision tree. But as was mentioned, 90% accuracy can be considered quite good..

Answer 5

90% is good or bad, depends on the domain of the data.

However, it might be that the classes in your data are overlapping and you can't really do more than 90%.

You can try to look in what nodes are the errors, and check if it's possible to improve the classification by changing them.

You can also try Random Forest.